cluster/afr: Init local on txn-frame for zerofill

Change-Id: I516f4fb0237dd0b3e512117bf987cea69f8678b8
BUG: 1084485
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7407
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>