Merge #11512: Use GetDesireableServiceFlags in seeds, dnsseeds, fixing static seed adding

2b839ab Update chainparams comment for more info on service bits per dnsseed (Matt Corallo)
62e7642 Fall back to oneshot for DNS Seeds which don't support filtering. (Matt Corallo)
51ae766 Use GetDesireableServiceFlags in static seeds, document this. (Matt Corallo)
fb6f6b1 bluematt's testnet-seed now supports x9 (and is just a static list) (Matt Corallo)

Pull request description:

  4440710 broke inserting entries into addrman from dnsseeds which
  did not support service bits, as well as static seeds. Static seeds
  were already being filtered by UA for 0.13.1+ (ie NODE_WITNESS), so
  simply changing the default service bits to include NODE_WITNESS
  (and updating docs appropriately) is sufficient. For DNS Seeds, not
  supporting NODE_WITNESS is no longer useful, so instead use
  non-filtering seeds as oneshot hosts irrespective of named proxy.

  I've set my testnet-seed to also support x9, though because it is simply a static host, it may be useful to leave the support off so that it is used as a oneshot to get addresses from a live node instead. I'm fine with either.

Tree-SHA512: 3f17d4d2b0b84d876981c962d2b44cb0c8f95f52c56a48c6b35fd882f6d7a40805f320ec452985a1c0b34aebddb1922709156c3ceccd1b9f8363fd7cb537d21d

contrib/seeds/README.md

@@ -4,7 +4,9 @@ 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.
+and remove old versions as necessary (at a minimum when GetDesireableServiceFlags
+changes its default return value, as those are the services which seeds are added
+to addrman with).
 
 The seeds compiled into the release are created from sipa's DNS seed data, like this: