Merge PR #18787 into master

* refs/pull/18787/head:
	mds: prevent filelock from being stuck at XSYN state
	mds: implement LOCK_XSYN_LOCK and LOCK_XSYN_MIX
	mds: cleanup set/drop loner code

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>

diff --cc src/mds/CInode.cc
Simple merge

diff --cc src/mds/CInode.h
Simple merge

diff --cc src/mds/Locker.cc
Simple merge