Added support for passing custom Remote ID in Option 82

Copypaste from mail:
Hi!
Manpage of dhcrelay says:
"The client supports inclusion of a Remote ID  suboption as well, but this is not used by default."

But there's no support of setting Remote ID in Option 82 at dhcrelay. I think this would be really usefull. I need central DHCP server with relays in my company. We use manageable switches with Option 82 support, these are OK (they're including RemoteID of switch and CircuitID of port to DHCP requests). But in some places without these switches we need to use Linux with dhcrelay instead (CircuitID identifies interface as needed, but we also need to set RemoteID as we have multiple relays in our network, which means shitloads of conflicting eth0s and eth1s)

So i really need to append different RemoteIDs set by commandline argument on each relay...

Right now i am going to make some ugly dirty adhoc patch to dhcrelay, but i guess you can do it much better... Do you think it's possible to get this improvement in official release?