Increase the buffer size of mDNS socket handlers.

The current buffer size often induces ERR_MSG_TOO_BIG and increases the
chance that we miss expected messages.

Bug: 993770
Change-Id: I067782f0aa287627a6948b0286771d3fe54aef18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1757395Reviewed-by: Eric Orth <ericorth@chromium.org>
Commit-Queue: Qingsi Wang <qingsi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687687}

services/network/mdns_responder.cc

@@ -409,7 +409,7 @@ class MdnsResponderManager::SocketHandler {
         socket_(std::move(socket)),
         responder_manager_(responder_manager),
         io_buffer_(base::MakeRefCounted<net::IOBufferWithSize>(
-            net::dns_protocol::kMaxUDPSize + 1)) {}
+            net::dns_protocol::kMaxMulticastSize + 1)) {}
   ~SocketHandler() = default;
 
   int Start() {