GFS2: rm on multiple nodes causes panic

This patch fixes a problem whereby simultaneous unlink, rmdir,
rename and link operations (e.g. rm -fR *) from multiple nodes
on the same GFS2 file system can cause kernel panics, hangs,
and/or memory corruption.  It also gets rid of all the non-rgrp
calls to gfs2_glock_nq_m.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>