rpc: fix typo which refers glibc macro

A typo which read MAX_AUTH_BYTES instead of GF_MAX_AUTH_BYTES was
picking the value 400 instead of the larger 2048. This causes
failures when number of aux group ids is a large number.

Change-Id: Idb8d59aee2690fd53e24c2e09f58a16fe387ef27
BUG: 1000131
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5854
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>