Support DNS resolution matching a specified IP family.

The input SocketAddress for STUN host lookup is constructed with just
the hostname, so the family is AF_UNSPEC. So added an overload with a
target family to distinguish this from the family of the input addr.

Bug: webrtc:14319, webrtc:14131
Change-Id: Ia5ac5aa2e894e0c4dfb4417e3e8a76a6cec3ea71
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/270624
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Sameer Vijaykar <samvi@google.com>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@google.com>
Cr-Commit-Position: refs/heads/main@{#37750}
diff --git a/rtc_base/async_resolver.h b/rtc_base/async_resolver.h
index b7125ba..46be438 100644
--- a/rtc_base/async_resolver.h
+++ b/rtc_base/async_resolver.h
@@ -45,6 +45,7 @@
   ~AsyncResolver() override;
 
   void Start(const SocketAddress& addr) override;
+  void Start(const SocketAddress& addr, int family) override;
   bool GetResolvedAddress(int family, SocketAddress* addr) const override;
   int GetError() const override;
   void Destroy(bool wait) override;