nfs: prevent NFS server crash when upgrading from 3.2.x server

After an upgrade the NFS3 filehandle size changed (became smaller),
but when doing a live ugprade the client would send the old handle
(expect ESTALE and do fresh lookup). But when reading the old
handle we were reading it into a structure which was limited to the
size of the new handle, while we should have been reading into a
buffer which is as big as the NFS3 spec permits the handle size to
be. The actor functions declare the structure on the stack. So the
overflow is resulting in a stack corruption.

Change-Id: Ie930875ac9db46b43d1cb8ad1e6d89cdaeded7ca
BUG: 1002385
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5730
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>