p2p: add only reachable addresses to addrman

We will not make outgoing connection to peers that are unreachable
(e.g. because of -onlynet configuration).
Therefore, it makes no sense to add them to addrman in the first place.
While this is already the case for addresses received via p2p addr
messages, this commit does the same for addresses received
from fixed seeds.

Author: mzumsande

src/net.cpp

@@ -1635,10 +1635,15 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
             }
 
             if (add_fixed_seeds_now) {
+                std::vector<CAddress> seed_addrs{ConvertSeeds(Params().FixedSeeds())};
+                seed_addrs.erase(std::remove_if(seed_addrs.begin(), seed_addrs.end(),
+                                               [](const CAddress& addr) { return !IsReachable(addr); }),
+                                seed_addrs.end());
                 CNetAddr local;
                 local.SetInternal("fixedseeds");
-                addrman.Add(ConvertSeeds(Params().FixedSeeds()), local);
+                addrman.Add(seed_addrs, local);
                 add_fixed_seeds = false;
+                LogPrintf("Added %d fixed seeds from reachable networks.\n", seed_addrs.size());
             }
         }