VPP-163 "show ip6 interface" ignores many addresses

VPP-163 "show ip6 interface" ignores many addresses

The output of the CLI command "show ip6 interface" shows only the first
link-local address and any globally-scoped addresses. It ignores all
other valid address scopes.

This patch reworks that routine to cover the three main address scopes
("link-local", "global" and "local") and anything else it finds is
grouped under "other").

Rationale for this final grouping is that these other addresses fall under
ranges currently either "reserved" or "multicast" in scope. Whilst it's
good to show if these are present, they are not normally found as link
addresses.

DBGvpp# sh ip6 int tap-0
tap-0 is admin down
	Link-local address(es):
		fe80::e857:7fff:fe77:c1a9/64
	Local unicast address(es):
		fd50:7389:246b:4321::2/64
	Joined group address(es):
		ff02::1
		ff02::2
		ff02::16
		ff02::1:ff77:c1a9
		ff02::1:ff00:2
...

Change-Id: I1d750b3b39c54aa4eb75632d53089640601bcba5
Signed-off-by: Chris Luke <chrisy@flirble.org>