stats: add dtlsRole to transport

https://w3c.github.io/webrtc-stats/#dom-rtctransportstats-dtlsrole

BUG=webrtc:13978

Change-Id: Ib158427d2df0307884381bdd46c411f60f56a371
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/259761
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/main@{#36730}
diff --git a/pc/rtc_stats_integrationtest.cc b/pc/rtc_stats_integrationtest.cc
index 956f414..07a8bdc 100644
--- a/pc/rtc_stats_integrationtest.cc
+++ b/pc/rtc_stats_integrationtest.cc
@@ -1136,6 +1136,7 @@
                                      RTCCertificateStats::kType);
     verifier.TestMemberIsDefined(transport.tls_version);
     verifier.TestMemberIsDefined(transport.dtls_cipher);
+    verifier.TestMemberIsDefined(transport.dtls_role);
     verifier.TestMemberIsDefined(transport.srtp_cipher);
     verifier.TestMemberIsPositive<uint32_t>(
         transport.selected_candidate_pair_changes);