reschedule iface even when send fails

Not rescheduling can leave the iface as the next iface to expire
which will peg the CPU at 100% if sending continues to fail.  This
change logs the failure and reschedules like normal when the iface
failes to send an ra.

Conflicts:
	radvd.c
Update CHANGES and VERSION for radvd 1.9.9
fix the contributers list in the man page