Add functionality for sending and 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
the remote status are the remote node's clock, and the 32nd bit of
the remote status is the failure status (0 for failed, 1 for alive).
The local status is simply the local clock, which uses all 32 bits.

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.

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.
Add efficient monitoring functionality

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.
Enable receipt and processing of monitoring packets

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.

Since monitoring packets may now be received, it is possible
for monitoring to be successful (the target responds). Hence,
end_interval_success() is added.
Fix spelling of announcement

All uses of NWP_TYPE_ANNOUNCEMENT have been fixed for spelling.