RFC 4191 Default Router Preference support for router advertisements

Adds "ipv6 nd router-preference (high|medium|low)" and
"no ipv6 nd router-preference" interface commands.

Files modified:

   doc/ipv6.texi
   zebra/interface.c
   zebra/interface.h
   zebra/rtadv.c
   zebra/rtadv.h

Signed-off-by: Chris Caputo <ccaputo@alt.net>
5 files changed