lib, pimd: add address match mode to prefix lists

lib, pimd: add address match mode to prefix lists

... the PIM code is kinda misusing prefix lists to match addresses.
Considering the weird semantics of access-lists, I can't fault it.
However, prefix lists aren't great at matching addresses by default,
since they try to match the prefix length too.  So, here's an "address
match mode" for prefix lists to get that to work more reasonably.

Fixes: #8492
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>