Avoid unlocking unlocked mutex in RCTL jail code.  Specific test case
is attached to PR.

PR:		193457
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271317 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f