routing: Make ip[6]_tryforward() FIB-aware for local traffic

ip_tryforward() and ip6_tryforward() checks whether the destination
address is local or not without considering if it belongs to the current FIB.
If the destination is local but not in our FIB, forward it instead
of returning it to ip_input().

PR: 292319
Reviewed by: zlei
MFC after: 1 week
MFC to: stable/15
Differential Revision: https://reviews.freebsd.org/D56353