Locker: accept ctime updates from clients without dirty write caps

The ctime changes any time the inode does. That can happen even without
the file itself having changed, so we'd better accept the update whenever
the auth caps have dirtied, without worrying about the file caps!

Fixes: #9514
Backport: firefly

Signed-off-by: Greg Farnum <greg@inktank.com>
Reviewed-by: Sage Weil <sage@redhat.com>
Reviewed-by: John Spray <john.spray@redhat.com>