Remove the last hacks concerning the global list of IPv4 addresses in the

Remove the last hacks concerning the global list of IPv4 addresses in the
source address selection logic.

These hacks were only relevant for the NFS diskless boot code in order to
pick the local broadcast address of the only configured interface.  So, be
explicit and set this address directly.

Tested by florian@, ok henning@, beck@, chrisz@