MT#60408 SdpMedia: initialize port and nports to 0

Explicitly set port and nports to 0 when initializing
a brand new instance of SdpMedia.

This resolves warnings:

../../core/AmSdp.h:168:8: warning: '*(__vector(2) unsigned int*)((char*)&<unnamed> + offsetof(SdpMedia, SdpMedia::port))' may be used uninitialized [-Wmaybe-uninitialized]
  168 | struct SdpMedia
      |        ^~~~~~~~

 ../../core/AmSdp.h:168:8: warning: '<unnamed>.SdpMedia::nports' may be used uninitialized [-Wmaybe-uninitialized]
  168 | struct SdpMedia

Change-Id: Ifa2838ba0ef2f1a48b4fdc07b7bfaf8c5aefcfaa

core/AmSdp.h

@@ -192,7 +192,7 @@ struct SdpMedia
 
   bool operator == (const SdpMedia& other) const;
 
-  SdpMedia() : conn(), dir(DirUndefined), type(MT_NONE), transport(TP_NONE), send(true), recv(true) {}
+  SdpMedia() : port(0), nports(0), conn(), dir(DirUndefined), type(MT_NONE), transport(TP_NONE), send(true), recv(true) {}
 
   /** pretty print */
   string debugPrint() const;