Add functionality for maintaining neighbor status

struct hrdw_addr needs fields describing the local and remote status
(failure status and clock time) of a neighbor. The first 31 bits of
remote_sc are the remote node's clock, and the 32nd bit of remote_rc
is the failure status (0 for failed, 1 for alive). local_c is 32
bits of the local clock.

All clock times are the lower 32 bits of the wall time, measured in
seconds.

Since the 32 bits of the status are split up, functions
set_remote_status() and set_remote_clock() are added to ensure users
safely update these fields using bit masks.

Because neighbors now have a status associated with them, NWP
needs methods of disseminating that information. To do this,
the routines for announcing and sending neighbor lists must
be amended to include status information, and the packet definitions
for announcements and neighbor lists must be amended. A node will
only send information about a failed neighbor if it is within a
time bound defined by NWP_LIST_TIME_MAX so that failed neighbors
are not cyclically added and deleted from neighbor lists in the LAN.

Status information can be taken from announcement and neighbor list
packets in read_announcement() and process_neigh_list(), and can be
passed to functions that create and insert neighbors, such as
new_ha(), add_ha(), and insert_neigh().

main_newroute() in net/xia/ppal_hid/main.c must also be altered
to match the change in function signature for insert_neigh(),
and the function prototype must be changed in
include/net/xia_hid.h.
Move error checks for packet dropping

struct general_hdr is not general enough for all types of NWP
packets; only the first two fields are necessary. Therefore, the
error-checking code for the number of HIDs and the hardware
address length should be moved to more local code for
announcements and neighbor lists.
Implement efficient monitoring algorithm

Every struct hid_dev now has a timer to periodically begin a
monitoring interval. It is also necessary to allocate memory
for a temporary target for each monitoring interval.

There are also bools for whether monitoring is currently
occuring, for determining whether contact has been made with
any neighbor during the current monitoring interval (to
diagnose network partitions), and for whether the neighbor has
yet been remonitored if failure is suspected.

Upon arrival of a neighbor list, the monitoring algorithm may
begin in process_neigh_list(). monitor() initiates a monitoring
interval, using pick_random_neigh() to select a random target
to monitor.

To accomplish this, the monitoring algorithm first pings the
selected target, which may result in a timer expiration and
callback of end_ping_failure(). In that case, investigative
neighbors may be used to verify that the given target has
failed. If, at the end of the investigative time period, no
response from the target has been received, a timer expiry
callbacks into end_interval_failure(), which may declare a
node as failed.

The forward declaration of end_interval_failure() is necessary
because of the cyclic nature between monitor(),
end_ping_failure(), and end_interval_failure().

In order to send monitoring packets, send_monitoring() is
implemented. Note that const u8 *inv should not be used
for Ping and Ack packets, and in those cases should be set to
NULL.

A function find_update_neigh_sc() is added to update the status
of a hardware address for which we don't have a struct
hrdw_addr reference.

nwp_rcv() may now accept monitoring packets and distribute
them to process_monitoring(), which updates clocks, changes
timers, and dispatches packets as necessary depending on the
type of packet that has been received. When a monitoring
iteration is successful (an Ack is received), the monitoring
interval will end in end_interval_success().
Add functionality for cleaning neighbor list

NWP monitoring has the power to detect and declare interfaces and
neighboring HIDs as failed. To do this, clean_neigh_list() is
periodically called by a timer in each hdev to clean the neighbor
list of any failed nodes that have also been declared failed for
at least NWP_FAILED_TTL seconds.
Fix spelling of announcement

Fixed all spelling mistakes for "announcement."