packets: Generalize reserved RSPAN protocols.

packets: Generalize reserved RSPAN protocols.

Open vSwitch refuses to mirror certain destination addresses in
addition to those classified by eth_addr_is_reserved().  Looking
through the uses of eth_addr_is_reserved(), one finds that no
callers should be using the additional addresses which mirroring
drops.  This patch folds the additional addresses dropped in the
mirroring code, into the more general eth_addr_is_reserverd()
function.

This patch also changes the implementation in a way that is
slightly less efficient, but much easier to read and extend int he
future.

Bug #11755.
Signed-off-by: Ethan Jackson <ethan@nicira.com>