[Bro] help for adding new packet filter

[Vern Paxson]

> line 1: run-time error: precompile_pcap_filter: pcap_compile((((gre) or (udp)) or (tcp)) or (icmp)): parse error
>  can't compile filter (((gre) or (udp)) or (tcp)) or (icmp)

The problem is that tcpdump (at least my version) doesn't have a "gre"
keyword.  So, to specify that you want to capture GRE traffic, you'll need
to describe it dirctly in terms of the IP "protocol" field (e.g., "tcp"
is the same as "ip proto 6").

		Vern