webrtc wpt: include mid extension in hardcoded sdp offer

which is mandatory to implement per
https://datatracker.ietf.org/doc/html/rfc8853#section-5.5

BUG=chromium:1422258

Change-Id: I5e7aa380302a84775567658628c1142fa7004355
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4571057
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1151835}
diff --git a/webrtc/simulcast/setParameters-encodings.https.html b/webrtc/simulcast/setParameters-encodings.https.html
index ac04ca5..86274a0 100644
--- a/webrtc/simulcast/setParameters-encodings.https.html
+++ b/webrtc/simulcast/setParameters-encodings.https.html
@@ -183,7 +183,8 @@
 a=fingerprint:sha-256 5B:D3:8E:66:0E:7D:D3:F3:8E:E6:80:28:19:FC:55:AD:58:5D:B9:3D:A8:DE:45:4A:E7:87:02:F8:3C:0B:3B:B3
 a=setup:actpass
 a=mid:0
-a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
+a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
+a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id
 a=recvonly
 a=rtcp-mux
 a=rtpmap:96 VP8/90000