net: Do not skip the I2P network from GetNetworkNames()

So that help texts include "i2p" in:
* `./bitcoind -help` (in `-onlynet` description)
* `getpeerinfo` RPC
* `getnetworkinfo` RPC

Co-authored-by: Jon Atack <jon@atack.com>

test/functional/rpc_net.py

@@ -105,7 +105,7 @@ class NetTest(BitcoinTestFramework):
         assert_equal(peer_info[1][1]['connection_type'], 'inbound')
 
         # Check dynamically generated networks list in getpeerinfo help output.
-        assert "(ipv4, ipv6, onion, not_publicly_routable)" in self.nodes[0].help("getpeerinfo")
+        assert "(ipv4, ipv6, onion, i2p, not_publicly_routable)" in self.nodes[0].help("getpeerinfo")
 
     def test_getnettotals(self):
         self.log.info("Test getnettotals")
@@ -156,7 +156,7 @@ class NetTest(BitcoinTestFramework):
             assert_net_servicesnames(int(info["localservices"], 0x10), info["localservicesnames"])
 
         # Check dynamically generated networks list in getnetworkinfo help output.
-        assert "(ipv4, ipv6, onion)" in self.nodes[0].help("getnetworkinfo")
+        assert "(ipv4, ipv6, onion, i2p)" in self.nodes[0].help("getnetworkinfo")
 
     def test_getaddednodeinfo(self):
         self.log.info("Test getaddednodeinfo")