net: tcp2: Send TCP data to caller

Add a net_context backpointer and receiver user data to the tcp
structure. Once the desired callback and user data is set in
net_tcp_recv(), net_context_packet_received() can be called at
TCP reception in tcp_data_get(), moving the TCP data to the
recipient. IP and TCP protocol headers are sent as NULL, they
are not used by e.g. the socket code.

Signed-off-by: Patrik Flykt <patrik.flykt@intel.com>
Signed-off-by: Oleg Zhurakivskyy <oleg.zhurakivskyy@intel.com>