tcp: add tcp_conn_request

Create tcp_conn_request and remove most of the code from
tcp_v4_conn_request and tcp_v6_conn_request.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/net/tcp.h
Simple merge

diff --cc net/ipv4/tcp_input.c
Simple merge

diff --cc net/ipv4/tcp_ipv4.c
Simple merge

diff --cc net/ipv6/tcp_ipv6.c
Simple merge