lacp: review follow-ups

lacp_in() always leaves uip_len at 0, so the tcpip_output() after it
never ran. The LAG page names the active members by front-panel port
instead of a logical mask. The partner key is not part of selection;
say so under Known limits.

rtlplayground.c

@@ -1071,8 +1071,6 @@ void handle_rx(void)
 				}
 			} else if (lacpEnabled && uip_buf[5] == 0x02) {	// LACPDU (slow protocols)
 				lacp_in();
-				if (uip_len)
-					tcpip_output();
 			}
 		} else if (igmpEnabled && uip_buf[0] == 0x01 && uip_buf[1] == 0x00 && uip_buf[2] == 0x5e // IPv4-MC packet?
 			&& igmp_packet_handler()) {