snaplen is too small for jumbo frames

topic/jazoff/fix-snaplen in broctl and bro change the default snaplen from 8192 to 9216

The default snaplen is too small to handle jumbo frames properly.

Also.. I'm not sure if the pcap variables in broctl should default to anything.. with the options defaulting to a value you can't override the snaplen with a redef in bro script since the broctl-config.bro file pushed out by broctl will override it.