Fix xdr_to_generic success check

Fix xdr_to_generic success check

This patch fixes the success check for xdr_to_generic function across the
codebase.

Also, cleans up the brick_op actors table in glusterfsd-mgmt.c to make sure that
the actors are called directly by rpcsvc.

Change-Id: I3086585f30c44f69f1bc83665f89e30025f76d3a
BUG: 884452
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/4278
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>