mesh portal discovery

[John Watlington]

Right now we have a problem with mesh portal discovery.

The DHCP procedure currently being used only discovers
the nearest mesh portal when it is first run (DHCP_DISCOVER),
not when it tries to renew (DHCP_REQUEST).   Furthermore,
as the address previously assigned indicates which mesh portal
was selected, it seems like we should always be discovering, not
renewing...

There are larger issues which will probably need a day of discussion
later surrounding IPv6 deployment, such as cooperation between RADVD
and mesh portal discovery...   (Please defer discussion on this right  
now)

wad