Use const rtc::Network* in ports and port allocator

No-try: True
Bug: webrtc:13869
Change-Id: I6004fa96278263d0d25a1446d7bb8de41a563433
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/256682
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@google.com>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36353}
diff --git a/p2p/base/port_interface.h b/p2p/base/port_interface.h
index 73c8e36..02fd979 100644
--- a/p2p/base/port_interface.h
+++ b/p2p/base/port_interface.h
@@ -49,7 +49,7 @@
   virtual ~PortInterface();
 
   virtual const std::string& Type() const = 0;
-  virtual rtc::Network* Network() const = 0;
+  virtual const rtc::Network* Network() const = 0;
 
   // Methods to set/get ICE role and tiebreaker values.
   virtual void SetIceRole(IceRole role) = 0;