Set ack and ackreturn to 0 for local packets always

This won't really have any in-game effect, this is just so the debugfile doesn't display the ack values of the PREVIOUS sent/got packet

src/d_net.c

@@ -1028,6 +1028,7 @@ boolean HSendPacket(INT32 node, boolean reliable, UINT8 acknum, size_t packetlen
 #endif
 			return false;
 		}
+		netbuffer->ack = netbuffer->ackreturn = 0; // don't hold over values from last packet sent/received
 		M_Memcpy(&reboundstore[rebound_head], netbuffer,
 			doomcom->datalength);
 		reboundsize[rebound_head] = doomcom->datalength;