net: tcp: fix ECONNREFUSED not reported by zsock_connect

When a TCP connection is refused during zsock_connect, errno is set
to -ENOTCONN, but errno should be set to -ECONNREFUSED. This change
causes the ECONNREFUSED status to be propagated from tcp_in to
net_tcp_connect, which eventually causes errno to be set
to -ECONNREFUSED.

Signed-off-by: Noah Olson <noah@wavelynx.com>