protocol: Log ENODATA & ENOATTR logs at DEBUG loglevel in removexattr_cbk.

Prevents messages of the following type from being seen by default in the log files:

[2014-09-19 07:57:39.877806] W
[client-rpc-fops.c:1232:client3_3_removexattr_cbk] 0-<volume_name>-client-0:
remote operation failed: No data available
[2014-09-19 07:57:39.877963] W
[client-rpc-fops.c:1232:client3_3_removexattr_cbk] 0-<volume_name>-client-1:
remote operation failed: No data available

Change-Id: I3b1a121b0fc272eb772547275bb8085ed19db5a1
BUG: 1144527
Signed-off-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/8781
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>