fs: dlm: rsb hash table flag value to atomic ops

This patch moves the rsb hash table handling to atomic flag operations.
The flag operations for DLM_RTF_SHRINK are protected by
ls->ls_rsbtbl[b].lock. However we switch to atomic ops if new possible
flags will be used in a different way and don't assume such lock
dependencies.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>