Move SendBindingResponse to Connection

This patch moves the SendBindingResponse from Port
to Connection. This is a behavioural NOP, and I don't
understand why it was in Port in the firs place!

Found when working on GOOG_PING.

BUG=webrtc:11100

Change-Id: I0466c5381f08ec4926ca3380e6914f0bc0dfcf63
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161081
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29963}

p2p/base/port.h

diff --git a/p2p/base/port.h b/p2p/base/port.h
index d609922..84340e8 100644
--- a/p2p/base/port.h
+++ b/p2p/base/port.h
@@ -287,11 +287,7 @@
   virtual bool CanHandleIncomingPacketsFrom(
       const rtc::SocketAddress& remote_addr) const;
 
-  // Sends a response message (normal or error) to the given request.  One of
-  // these methods should be called as a response to SignalUnknownAddress.
-  // NOTE: You MUST call CreateConnection BEFORE SendBindingResponse.
-  void SendBindingResponse(StunMessage* request,
-                           const rtc::SocketAddress& addr) override;
+  // Sends a response error to the given request.
   void SendBindingErrorResponse(StunMessage* request,
                                 const rtc::SocketAddress& addr,
                                 int error_code,