dlm: Use cmwq for send and receive workqueues

So far as I can tell, there is no reason to use a single-threaded
send workqueue for dlm, since it may need to send to several sockets
concurrently. Both workqueues are set to WQ_MEM_RECLAIM to avoid
any possible deadlocks, WQ_HIGHPRI since locking traffic is highly
latency sensitive (and to avoid a priority inversion wrt GFS2's
glock_workqueue) and WQ_FREEZABLE just in case someone needs to do
that (even though with current cluster infrastructure, it doesn't
make sense as the node will most likely land up ejected from the
cluster) in the future.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: David Teigland <teigland@redhat.com>