sys_net improvements

[RipleyTom]

Various improvements focused on P2PS sockets:

• Fixes SYN|ACK being sent from the listening socket instead of the newly created socket(because of this it kept being sent and was never cleared, breaking further connections as it spammed connection received with wrong seq being sent).
• Added static incremental vport assignment instead of always starting at 30000 and finding the first one free.
• Add proper disconnection mechanism, clearing all pending packets and clearing connected state from relevant maps.
• Add extra check for EAGAIN on the p2ps sockets as there can be sendto concurrency on the socket from the tcp timeout monitor thread. Now we keep trying until it goes through or another error happens.
• Send RST on receiving a valid P2PS packet aimed at a non-existent socket.
• Signaling: signal connection closed when it's terminated by peer.