Add a flag to actively reset the SRTP parameters

Add a new flag to RtcConfiguration. By setting that flag to true, the
SRTP parameters will be reset whenever the DTLS transports are reset
after every offer/answer negotiation.

This should only be used as a workaround for the linked bug, if the
application knows that the other party is affected (for instance,
using a version number).

Bug: chromium:835958
Change-Id: Ifb4b99f68dc272507728ab59c07627f0d1b9c605
Reviewed-on: https://webrtc-review.googlesource.com/81642
Commit-Queue: Zhi Huang <zhihuang@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23570}

api/peerconnectioninterface.h

@@ -577,6 +577,13 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
     // For all other users, specify kUnifiedPlan.
     SdpSemantics sdp_semantics = SdpSemantics::kPlanB;
 
+    // Actively reset the SRTP parameters whenever the DTLS transports
+    // underneath are reset for every offer/answer negotiation.
+    // This is only intended to be a workaround for crbug.com/835958
+    // WARNING: This would cause RTP/RTCP packets decryption failure if not used
+    // correctly. This flag will be deprecated soon. Do not rely on it.
+    bool active_reset_srtp_params = false;
+
     //
     // Don't forget to update operator== if adding something.
     //