treat "default" and "all"/"any" addresses differenty

treat "default" and "all"/"any" addresses differenty

Debian maintainer found that basic command:
	# ip route flush all
No longer worked as expected which breaks user scripts and
expectations. It no longer flushed all IPv4 routes.

Recently behavior of "default" prefix parameter was corrected. But at
the same time behavior of "all"/"any" was altered too, because they
were the same branch of the code. As those parameters mean different,
they need to be treated differently in code too. This patch reflects
the difference.

Also after mentioned change, address parsing code was changed more
and address family was set explicitly even for "all"/"any" addresses.
And that broke matching conditions further. This patch fixes that too
and returns AF_UNSPEC to "all"/"any" address.

Now "default" is treated as top-level prefix (for example 0.0.0.0/0 in
IPv4) and "all"/"any" always matches anything in exact, root and match
modes.

Reported-by: Luca Boccassi <bluca@debian.org>
Signed-off-by: Alexander Zubkov <green@msu.ru>