ipasdv4/tcp_ipv4: remove redundant assignment

The value of 'st->state' has been verified as "TCP_SEQ_STATE_LISTENING",
it's unnecessary to assign TCP_SEQ_STATE_LISTENING to it, so we can remove it.

Signed-off-by: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>