Fix deadlock with Driver::write

Use a spin lock to recheck the queue size until it has room to push.

platform/windows/pcap.cpp

@@ -297,7 +297,6 @@ void PCAP::writeTask() {
 		auto bs = sendPacket.getBytestream();
 		if(!closing)
 			pcap.sendpacket(interface.fp, bs.data(), (int)bs.size());
-		onWrite();
 		// TODO Handle packet send errors
 	}
 }

platform/windows/vcp.cpp

@@ -401,8 +401,6 @@ void VCP::writeTask() {
 				bytesWritten = 0;
 				if(WriteFile(handle, writeOp.bytes.data(), (DWORD)writeOp.bytes.size(), nullptr, &overlappedWrite))
 					continue;
-
-				onWrite();
 				
 				auto winerr = GetLastError();
 				if(winerr == ERROR_IO_PENDING) {