Fix NDP table discovery for 6to4 interfaces.


git-svn-id: http://observium.org/svn/observer/trunk@4240 61d68cd4-352d-0410-923a-c4978735b2b8
exclude mac broadcast (ff:ff:ff:ff:ff:ff)


git-svn-id: http://observium.org/svn/observer/trunk@4241 61d68cd4-352d-0410-923a-c4978735b2b8