Added DLT choices for Fibre Channel interfaces

Added DLTs for interfaces with Fibre Channel ARPHRDs. 
Added dummy set_datalink for pcap-linux to allow setting DLT.

I'm not sure if adding set_datalink is a good thing to do. Netfilter seems to do something like that and I couldn't find a less intrusive way to patch this. 

Comments are of course welcome.