NFS: populate ->net in mount data when remounting

Otherwise the kernel oopses when remounting with IPv6 server because
net is dereferenced in dev_get_by_name.

Use net ns of current thread so that dev_get_by_name does not operate on
foreign ns. Changing the address is prohibited anyway so this should not
affect anything.
Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
Cc: linux-nfs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # 3.4+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/super.c

@@ -2260,6 +2260,7 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
 	data->nfs_server.addrlen = nfss->nfs_client->cl_addrlen;
 	data->version = nfsvers;
 	data->minorversion = nfss->nfs_client->cl_minorversion;
+	data->net = current->nsproxy->net_ns;
 	memcpy(&data->nfs_server.address, &nfss->nfs_client->cl_addr,
 		data->nfs_server.addrlen);