Move the predicted ports code out of rephist.c

It differs from the rest of the rephist code in that it's actually
necessary for Tor to operate, so it should probably go somewhere
else.  I'm not sure where yet, so I'll leave it in the same
directory, but give it its own file.

src/core/mainloop/mainloop.c

@@ -93,6 +93,7 @@
 #include "feature/rend/rendcache.h"
 #include "feature/rend/rendservice.h"
 #include "feature/stats/geoip.h"
+#include "feature/stats/predict_ports.h"
 #include "feature/stats/rephist.h"
 #include "lib/container/buffers.h"
 #include "lib/crypt_ops/crypto_rand.h"