new ATMIOCOPENVCC/CLOSEVCC. This allows us to not only use UBR channels
for IP over ATM, but also CBR, VBR and ABR. Change the format of the
link layer address to specify the channel characteristics. The old
format is still supported and opens UBR channels.
man page. This will be more scaleable as more driver man pages hit
the tree. Add also a description on how to do this configuration
in the rc.conf script.
