fuse-bridge: use READDIRPLUS support when available

This patch makes use of READDIRPLUS call when support is available
in the kernel.

Change-Id: Iac78881179567856b55af1f46594a2b2859309f0
BUG: 908128
Signed-off-by: Anand V. Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/3905
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>