Merge PR #27077 into master

Merge PR #27077 into master

* refs/pull/27077/head:
	test: check listattr for snapshot btime entry
	test: extend LibCephFS.Xattrs test
	client: remove unused vxattr length helpers
	client: fix _listxattr() vxattr buffer length calculation
	test: add libcephfs snap.btime xattr test
	client: add ceph.snap.btime vxattr
	mds: carry snapshot creation time with InodeStat

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