tcp: Reset tcp connections in SYN-SENT state

Userspace sends tcp connection (sock) destroy on network switch
i.e switching the default network of the device between multiple
networks(Cellular/Wifi/Ethernet).

Kernel though doesn't send reset for the connections in SYN-SENT state
and these connections continue to remain.
Even as per RFC 793, there is no hard rule to not send RST on ABORT in
this state.

Modify tcp_abort and tcp_disconnect behavior to send RST for connections
in syn-sent state to avoid lingering connections on network switch.

Signed-off-by: Manoj Basapathi <manojbm@codeaurora.org>
Signed-off-by: Sauvik Saha <ssaha@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>