addrman: remove invalid addresses when unserializing

The Tor v2 addresses, left over from when Tor v2 was supported will be
unserialized as a dummy, invalid `::` (all zeros) IPv6 address. Remove
them so that they do not take up space in addrman.

src/addrman.h

@@ -448,6 +448,8 @@ public:
             LogPrint(BCLog::ADDRMAN, "addrman lost %i new and %i tried addresses due to collisions\n", nLostUnk, nLost);
         }
 
+        RemoveInvalid();
+
         Check();
     }
 
@@ -756,6 +758,9 @@ private:
     //! Update an entry's service bits.
     void SetServices_(const CService &addr, ServiceFlags nServices) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
+    //! Remove invalid addresses.
+    void RemoveInvalid() EXCLUSIVE_LOCKS_REQUIRED(cs);
+
     friend class CAddrManTest;
 };