fs: dlm: use dlm_recovery_stopped instead of test_bit

This patch will change to use dlm_recovery_stopped() which is the dlm way
to check if the LSFL_RECOVER_STOP flag in ls_flags by using the helper.
It is an atomic operation but the check is still as before to fetch the
value if ls_recover_lock is held. There might be more further
investigations if the value can be changed afterwards and if it has any
side effects.

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