Merge bitcoin/bitcoin#21825: net: add I2P hardcoded seeds

142e2da440 net: add I2P seeds to chainparamsseeds (Jon Atack)
e01f173fb9 contrib: add a few I2P seed nodes (Jon Atack)
ea269c7ef1 contrib: parse I2P addresses in generate-seeds.py (Jon Atack)

Pull request description:

  Follow-up to #21560 that updated the fixed seeds infra for BIP155 addresses and then added Tor v3 ones:

  - Update contrib/generate-seeds.py to parse I2P addresses

  - Add a few I2P nodes to contrib/seeds/nodes_main.txt

  - Run generate-seeds.py and add the I2P seeds to chainparamsseeds.h

  Reviewers, see contrib/seeds/README.md for more info and feel free to use the following CLI one-liner to check for and propose additional seeds for contrib/seeds/nodes_main.txt. You can also see how many I2P peers your node knows with cli -addrinfo.

  ```rake
  bitcoin-cli getnodeaddresses 0 | jq '.[] | (select(.address | contains(".b32.i2p"))) | .address' | sort
  ```

  I verified the I2P addresses are correctly BIP155-serialized/deserialized by building with all seeds removed from chainparamsseeds.h except those added here, restarting with `-datadir=newdir -dnsseed=0` and running rpc ` getnodeaddresses 0` that initially returns only the new I2P addresses.

ACKs for top commit:
  laanwj:
    ACK 142e2da440
  vasild:
    ACK 142e2da440

Tree-SHA512: 040576012d5f1f034e2bd566ad654a6fdfd8ff7f6b12fa40c9fda1e948ebf8417fcea64cfc14938a41439370aa4669bab3e97274f9d4f9a6906fa9520afa9cf8

contrib/seeds/generate-seeds.py

@@ -16,6 +16,7 @@ These files must consist of lines in the format
     <ip>:<port>
     [<ipv6>]:<port>
     <onion>.onion:<port>
+    <i2p>.b32.i2p:<port>
 
 The output will be two data structures with the peers in binary format:
 
@@ -52,6 +53,12 @@ def name_to_bip155(addr):
             return (BIP155Network.TORV3, vchAddr[:32])
         else:
             raise ValueError('Invalid onion %s' % vchAddr)
+    elif addr.endswith('.b32.i2p'):
+        vchAddr = b32decode(addr[0:-8] + '====', True)
+        if len(vchAddr) == 32:
+            return (BIP155Network.I2P, vchAddr)
+        else:
+            raise ValueError(f'Invalid I2P {vchAddr}')
     elif '.' in addr: # IPv4
         return (BIP155Network.IPV4, bytes((int(x) for x in addr.split('.'))))
     elif ':' in addr: # IPv6

contrib/seeds/nodes_main.txt

@@ -1188,3 +1188,13 @@ sys54sv4xv3hn3sdiv3oadmzqpgyhd4u4xphv4xqk64ckvaxzm57a7yd.onion:8333
 tddeij4qigtjr6jfnrmq6btnirmq5msgwcsdpcdjr7atftm7cxlqztid.onion:8333
 vi5bnbxkleeqi6hfccjochnn65lcxlfqs4uwgmhudph554zibiusqnad.onion:8333
 xqt25cobm5zqucac3634zfght72he6u3eagfyej5ellbhcdgos7t2had.onion:8333
+
+# manually added 2021-05 for minimal i2p bootstrap support
+72l3ucjkuscrbiiepoehuwqgknyzgo7zuix5ty4puwrkyhtmnsga.b32.i2p:8333
+c4gfnttsuwqomiygupdqqqyy5y5emnk5c73hrfvatri67prd7vyq.b32.i2p:8333
+gehtac45oaghz54ypyopim64mql7oad2bqclla74l6tfeolzmodq.b32.i2p:8333
+h3r6bkn46qxftwja53pxiykntegfyfjqtnzbm6iv6r5mungmqgmq.b32.i2p:8333
+hnbbyjpxx54623l555sta7pocy3se4sdgmuebi5k6reesz5rjp6q.b32.i2p:8333
+pjs7or2ctvteeo5tu4bwyrtydeuhqhvdprtujn4daxr75jpebjxa.b32.i2p:8333
+wwbw7nqr3ahkqv62cuqfwgtneekvvpnuc4i4f6yo7tpoqjswvcwa.b32.i2p:8333
+zsxwyo6qcn3chqzwxnseusqgsnuw3maqnztkiypyfxtya4snkoka.b32.i2p:8333