fuse: fix memory leak in fuse_getxattr()

The fuse_getxattr() function was not freeing fuse_state_t resulting in a
memory leak. As a result, when continuous writes (run dd command in a loop)
were done from a FUSE mount point, the OOM killer killed the client
process (glusterfs).

Manual backport of: http://review.gluster.org/#/c/5392/, provided
by Martin Svec <martin.svec@zoner.cz>.

BUG: 1112844
Change-Id: Ic723675c53384d48c79ad1b11b21c1b17fb56866
Reviewed-on: http://review.gluster.org/8164
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>