Pause/resume pacer from Call instead of via SendStreams.

BUG=webrtc:5073

Review URL: https://codereview.webrtc.org/1398443007

Cr-Original-Commit-Position: refs/heads/master@{#10271}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 457a61db616f17be54b32bc7d8bb781d53396f69
diff --git a/call/call.cc b/call/call.cc
index 2c80ccf..41b2c83 100644
--- a/call/call.cc
+++ b/call/call.cc
@@ -396,6 +396,7 @@
   // to guarantee a consistent state across streams.
   rtc::CritScope lock(&network_enabled_crit_);
   network_enabled_ = state == kNetworkUp;
+  channel_group_->SignalNetworkState(state);
   {
     ReadLockScoped write_lock(*send_crit_);
     for (auto& kv : video_send_ssrcs_) {