net: tcp: Remove NET_TCP_HDR() macro and direct access to net_buf

Remove NET_TCP_HDR() macro as we cannot safely access TCP header
via it if the network packet header spans over multiple net_buf
fragments.

Fixed also the TCP unit tests so that they pass correctly.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
10 files changed