tipc-config: add udp bearer support

A UDP bearer is configured as:
tipc-config -be=udp:localip[:localport:remoteip:remoteport]
If a device name is specified, tipc-config will try to find the
interface, and select the local address from this interface.
(First address assigned will be used)
The remote endpoint of a UDP unicast bearer can also be a dns name.
UDP bearer support requires increased limits of link/bearer/interface
names in tipc_config.h

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>