Allocate, initialize, and free new monitoring fields

Every struct hid_dev now has two timers; one to periodically
begin a monitoring interval, and one to periodically clean the
neighbor list by deleting failed interfaces and neighbors. We
also need to allocate memory for a temporary target for each
monitoring interval.

hid_dev_finish_destroy() needs to do the opposite of hdev_init()
by deleting the timers and freeing the memory of the hdev.
Add functionality for cleaning neighbor list

NWP monitoring has the power to detect and declare interfaces and
neighboring HIDs as failed. clean_neigh_list() is periodically
called by a timer in each hdev to clean the neighbor list of any
failed nodes by deleting them.
Define and alter functions for sending monitoring information

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.
Change creation and insertion of neighbors to use status

Every struct hrdw_addr must be created with a local and remote
status identifier. This information can be taken from
announcement and neighbor list packets in read_announcement()
and process_neigh_list() and 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().
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.

Note that the reserved field of monitoring packets MUST be
non-zero as a convention for acceptance by nwp_rcv().

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.