bind_addr: use keywords to pick special types of addresses

In addition to using dotted-decimal IP addresses and symbolic names for bind addresses, the following values can also be used:

• GLOBAL: picks a global (public) address
• SITE_LOCAL: an address starting with 192.168.x.x or 10.0.x.x
• LINK_LOCAL: a link local address, ie. starting with 169.x.x.x or 254.x.x.x
• NON_LOOPBACK (default if bind_addr is not defined): picks any non-loopback address

The address is picked from any of the interfaces (which are up) on the host.

Examples:

#1: <UDP bind_addr="GLOBAL"../> // picks a global IP address if available. If not, falls back to picking any non-loopback address

#2: -Djgroups.bind_addr=SITE_LOCAL // picks a site local IP address