Merge #9128: net: Decouple CConnman and message serialization

c7be56d net: push only raw data into CConnman (Cory Fields)
2ec935d net: add CVectorWriter and CNetMsgMaker (Cory Fields)
b7695c2 net: No need to check individually for disconnection anymore (Cory Fields)
fedea8a net: don't send any messages before handshake or after requested disconnect (Cory Fields)
d74e352 net: Set feelers to disconnect at the end of the version message (Cory Fields)