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).

Change-Id: I6ded1a4c25d26ceab0cb3b89ac81066cb51343ec
BUG: 988182
Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-on: http://review.gluster.org/5392
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>