mptcp: fix bit MPTCP_PUSH_PENDING tests

The MPTCP_PUSH_PENDING define is 6 and these tests should be testing if
BIT(6) is set.

Fixes: c2e6048f ("mptcp: fix race in release_cb")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>