afr: serialize modification of {entrylk,inodelk}_lock_count

Typically this lock was not needed in practice, but with
http://review.gluster.org/3842, this code gets executed in multiple
threads for different servers and we lose a count. This results in
leaked lock and a hang for a future transaction.

Change-Id: I377ed20e44f2a45cff522289dfef181f0653eca2
BUG: 765564
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4480
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>