[Core] Configure E1.31 Bridge mode to allow reception on both eth0 and wlan0

Previously bridge mode would only listen for multicast on the first
configured interface which could be wlan0 if it was the default
route.  This commit changes the code to call setsockopt() for both
eth0 and wlan0 if they are configured to allow E1.31 reception on
either interface.
[Core] Add debug message to help tracking down a bug