Add field trial to reduce max STUN check retransmissions from 8 to 6 in accordance with RFC 5389.

Bug: webrtc:10282
Change-Id: I19ac690e3388e2015792695cf7836cb727a4314b
Reviewed-on: https://webrtc-review.googlesource.com/c/120960
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26524}
diff --git a/p2p/base/stun_request.h b/p2p/base/stun_request.h
index 7994fb6..571abe1 100644
--- a/p2p/base/stun_request.h
+++ b/p2p/base/stun_request.h
@@ -148,6 +148,7 @@
   StunRequestManager* manager_;
   StunMessage* msg_;
   int64_t tstamp_;
+  bool in_rfc5389_retransmission_experiment_;
 
   friend class StunRequestManager;
 };