[AP-UTILS] option to bind to specific interface for trapd

[Christian Lambert]

I thought it would be nice to have an option to bind listening
for traps (port 162) on a specific interface rather than INADDR_ANY
for the socket.    I'm thinking of running the trapd on my linux NAT
box, so I don't want it to be listening on all interfaces for traps.
Right now I just replaced it directly in the source code, but I thought
it would be easy to implement something like "-i <interface>".

My .02