ospfd: no router ospf crash fix

ospfd: no router ospf crash fix

no router ospf triggers to cancel all threads
including read/write (receive/send packets) threads,
cleans up resources fd, message queue and data.

Last job of write (packet) thread invoked where the
ospf instance is referenced is not running nor
the socket fd valid.

Write thread callback should check if fd is valid and
ospf instance is running before proceeding to send a
message over socket.

Ticket:CM-20095
Testing Done:

Performed the multiple 'no router ospf' with the fix
in topology where the crash was seen.
Post fix the crash is not observed.

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>