tcp: fix: TCP timewait port reuse rfc compliance

tcp: fix: TCP timewait port reuse rfc compliance

This patch provides a fix for early-kill of timewait sockets that is based on
rfc's 1122, 6191.

The following commits provided a solution for port re-use. However, they
are not fully compliant with rfc 1122 4.2.2.13 ( Closing a connection )
and rfc 6191 (Reducing the TIME-WAIT State Using TCP Timestamps)

commit b092b77cf238ba ("tcp: Enable TCP timewait port use") introduced
a significant improvement by enabling TCP timewait port re-use.

commit ee1cb469b2dd ("tcp: fix port reuse with multiple listeners") fixed
usage of the wrong value for connection_index when searching for a
listener, by storing the state in tcp.flags.

Implementation details:
When a SYN is received during time-wait state, the code
checks whether all the requirements for accepting the SYN packet are
met. If they aren't, the SYN can't be accepted and the packet is dropped,
otherwise, connection is deleted and a new connection with same port
is opened.

Type: fix
Signed-off-by: Ofer Heifetz <oferh@marvell.com>
Signed-off-by: Yuval Caduri <cyuval@marvell.com>
Signed-off-by: Michal Kalderon <mkalderon@marvell.com>
Change-Id: I38a33c6e321c760d45ebec9154399e1c90dd0250