In icmp6_rip6_input(), once we have a lock, make sure the inp is

In icmp6_rip6_input(), once we have a lock, make sure the inp is
not freed.  This can happen since the list traversal and locking
was converted to epoch(9).  If the inp is marked "freed", skip it.

This prevents a NULL pointer deref panic in ip6_savecontrol_v4()
trying to access the socket hanging off the inp, which was gone
by the time we got there.

Reported by:	andrew
Tested by:	andrew
Approved by:	re (gjb)