Fixes Issue #157 (Router segfaults) (#159)

Found a number of problems with the router when compiling on linux

* Expected malloc()'ed memory to be zeroed resulting in segfault
* IPC_NOWAIT in iplayer loop means incoming traffic will be delayed until outgoing traffic is received.
* When configured with two BIP interfaces, broadcast loops ensue because the broacast traffic is not correctly filtered.  I think the safest thing to do here is to use the SO_BINDTODEVICE setsockopt.

apps/router/msgqueue.c

@@ -58,12 +58,12 @@ bool send_to_msgbox(MSGBOX_ID dest, BACMSG *msg)
     return true;
 }
 
-BACMSG *recv_from_msgbox(MSGBOX_ID src, BACMSG *msg)
+BACMSG *recv_from_msgbox(MSGBOX_ID src, BACMSG *msg, int flags)
 {
     int recv_bytes;
 
     recv_bytes =
-        msgrcv(src, msg, sizeof(BACMSG) - sizeof(MSGTYPE), 0, IPC_NOWAIT);
+        msgrcv(src, msg, sizeof(BACMSG) - sizeof(MSGTYPE), 0, flags);
     if (recv_bytes > 0) {
         return msg;
     } else {