Ignore martians in `bt-bep5` program.

test/bt-bep5.cpp

 #include <bittorrent/dht.h>
+#include <bittorrent/is_martian.h>
 #include <bittorrent/routing_table.h>
 
 #include <iostream>
@@ -187,7 +188,14 @@ int main(int argc, const char** argv)
 
             auto peers = [&] {
                 Progress p(ctx.get_executor(), "Getting peers");
-                return dht.tracker_get_peers(infohash, cancel, yield[ec]);
+                auto ps = dht.tracker_get_peers(infohash, cancel, yield[ec]);
+                // Remove martian endpoints (cant't use `remove_if` on sets).
+                for (auto it = ps.begin(); it != ps.end();)
+                    if (is_martian(*it))
+                        it = ps.erase(it);
+                    else
+                        it++;
+                return ps;
             }();
 
             if (!ec) {