bonjour: refactor _match_buddies_by_address

* Use `g_slist_find_custom` instead of manual search. `BonjourBuddy` doesn't have `NULL` data in `ips` list.
* Add `_find_match_buddies_by_address` to reduce copypaste.
* Change comparisons order to reduce nesting.

Testing Done:
Compile.

Reviewed at https://reviews.imfreedom.org/r/545/