Allow random IP number allocation to peer.

Allow random IP number allocation to peer.
Validate the peers suggested IP by attempting to make a routing table
entry.
Give up IPCP negotiation if the peer NAKs us with an unusable IP.
Always SIOCDIFADDR then SIOCAIFADDR when configuring the tun device.
Using SIOCSIFDSTADDR allows duplicate dst addresses (which we don't
want)!!!
Allow up to 200 interface names (was 50) (now that ppp can play server
properly).
Up the version number (1.5 -> 1.6).

Cosmetic:
  Log unexpected CCP packets in the CCP log rather than the ERROR log.
  Log unexpected Config Reqs in the appropriate LCP/IPCP/CCP log rather
  than the ERROR log.
  Log failed route additions and deletions with WARN, not TCPIP.
  Log the option id and length for unrecognised IPCP options.
  Change some .Sq to .Ar in the man page.