Initialize IPFW static rules rmlock with RM_RECURSE flag.

This lock was replaced from rwlock in r272840. But unlike rwlock, rmlock
doesn't allow recursion on rm_rlock(), so at this time fix this with
RM_RECURSE flag. Later we need to change ipfw to avoid such recursions.

PR:		[[ https://bugs.freebsd.org/216171 | 216171 ]]