Added the common test setup.

Added a method to the Neighbor Solicitation Processing IsRouterFlag
tests, which performs the 'common test setup'.
Fixed a spelling mistake
Allow for more than one Neighbor solictation
Fixed assignment problem
Fixed a couple of silly mistakes
Used the correct (confusingly named) assert
Addresses in packet construction must be strings
Send the right option type in the Neighbor Advertisement
ll_addr is sometimes a method.
The destination link-layer should be TR2's