* refactor: make tr_peerIoSetEnabled() a member method
* refactor: make tr_peerIoFlushOutgoingProtocolMsgs() a member method
* refactor: make tr_peerIoFlush() a member method
* refactor: make tr_peerWriteBytes() a member method
* refactor: make tr_peerWriteBuf() a member method
* refactor: make tr_peerIoGetWriteBufferSpace() a member method
* chore: remove unused declaration
* refactor: make tr_peerIoUtpInit() a member method
* refactor: make tr_peerIoNew() a member method
* refactor: make tr_peerIoNewOutgoing() a member method
* refactor: make tr_peerIoNewIncoming() a member method