mptcp: zero token hash at creation time.

Otherwise the 'chain_len' filed will carry random values,
some token creation calls will fail due to excessive chain
length, causing unexpected fallback to TCP.

Fixes: 2c5ebd00 ("mptcp: refactor token container")
Reviewed-by: NMat Martineau <mathew.j.martineau@linux.intel.com>
Tested-by: NChristoph Paasch <cpaasch@apple.com>
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mptcp/token.c

@@ -368,7 +368,7 @@ void __init mptcp_token_init(void)
 					     sizeof(struct token_bucket),
 					     0,
 					     20,/* one slot per 1MB of memory */
-					     0,
+					     HASH_ZERO,
 					     NULL,
 					     &token_mask,
 					     0,