net: decouple state independent service flags from desirable ones

This former one will be moved to the peer manager class in the
following-up commit.

contrib/seeds/README.md

@@ -4,7 +4,7 @@ Utility to generate the seeds.txt list that is compiled into the client
 (see [src/chainparamsseeds.h](/src/chainparamsseeds.h) and other utilities in [contrib/seeds](/contrib/seeds)).
 
 Be sure to update `PATTERN_AGENT` in `makeseeds.py` to include the current version,
-and remove old versions as necessary (at a minimum when GetDesirableServiceFlags
+and remove old versions as necessary (at a minimum when SeedsServiceFlags()
 changes its default return value, as those are the services which seeds are added
 to addrman with).