erdtlsconnection: Fix format string compiler warning on 32 bit architectures

openwebrtc-gst-plugins/ext/erdtls/src/erdtlsconnection.c:462:57: warning:
      format specifies type 'long' but the argument has type 'gint64'
      (aka 'long long') [-Wformat]
                LOG_DEBUG(self, "waiting for %ld usec", wait_time);
                                             ~~~        ^~~~~~~~~
                                             %lld