* When opening a live pcap, obtain the list of supported DLTs from
the BPF.
* Add pcap_list_datalinks() to obtain a list of supported DLTs
supported by the interface associated with the pcap descriptor.
* Add pcap_set_datalink() to set the current DLT of the pcap.
* Bump shlib 1.2 -> 1.3; new functions added.
From David Young <dyoung@ojctech.com>, with some minor changes by me.
from tcpdump.org, although with a slightly different signature.
The tcpdump.org version has no way to report an error string back
to the caller. This version takes an additional "errbuf" argument
(similar to pcap_open_*()).
