Broadcast fixes

Broadcast fixes
 - Treat 255.255.255.255 as an undefined address
 - Choose the first interface when sending a broadcast packet (fixes failing with STATUS_NETWORK_UNREACHABLE when trying to send a broadcast packet)
 - Fix a broadcast address check so 255.255.255.255 will also pass (fixes sending queued broadcast packets)
 - Now a broadcast packet can be successfully sent from an interface with a valid IP address (previously they could only be sent when the interface didn't have an NCE entry)

svn path=/trunk/; revision=42375