sdp: use g_strdup instead of strdup
../gst-libs/gst/sdp/gstsdpmessage.c: In function ‘gst_sdp_parse_rtpmap’:
../gst-libs/gst/sdp/gstsdpmessage.c:3450:13: warning: implicit declaration of function ‘strdup’; did you mean ‘g_strdup’? [-Wimplicit-function-declaration]
*name = strdup (*name);
^~~~~~
g_strdup
../gst-libs/gst/sdp/gstsdpmessage.c:3450:11: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
*name = strdup (*name);
^