net: tcp: Add initial support for TIMEWAIT timer

Right now in FIN_WAIT1 state, if we receive FIN+ACK message, then
tcp state changed to FIN_WAIT2 on ACK flag and immediately on FIN
flag state changed to TIME_WAIT. Then final ACK is prepared and sent
(in queue at-least) to peer. Again immediately state changed to
TCP_CLOSED, where context is freed. net_context_put frees context
and releases tcp connection. Final ACK packet which is in queue
is dropped.

As a side effect of freed ACK packet, peer device keep on sending
FIN+ACK messages (that's why we see a lot of "TCP spurious
retransimission" messages in wireshark). As a result
of context free (respective connection handler also removed), we see
lot of packets dropped at connection input handler and replying with
ICMP error messages (destination unreachable).

To fix this issue, timewait timer support is required. When tcp
connection state changed to TIMEWAIT state, it should wait until
TIMEWAIT_TIMETOUT before changing state to TCP_CLOSED. It's
appropriate to close the tcp connection after timewait timer expiry.

Note: Right now timeout value is constant (250ms). But it should
be 2 * MSL (Maximum segment lifetime).

Signed-off-by: Ravi kumar Veeramally <ravikumar.veeramally@linux.intel.com>