net: fix some documentation comments in UDPSocketPosix

They were saying that they set the flags in |socket_options_|,
but that is simply not true anymore.

BUG=None
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Review-Url: https://codereview.chromium.org/2819153002
Cr-Commit-Position: refs/heads/master@{#465557}
diff --git a/net/socket/udp_socket_posix.h b/net/socket/udp_socket_posix.h
index 3d71835..ba42e04 100644
--- a/net/socket/udp_socket_posix.h
+++ b/net/socket/udp_socket_posix.h
@@ -133,14 +133,13 @@
 
   const NetLogWithSource& NetLog() const { return net_log_; }
 
-  // Sets corresponding flags in |socket_options_| to allow the socket
-  // to share the local address to which the socket will be bound with
-  // other processes. Should be called between Open() and Bind().
+  // Call this to enable SO_REUSEADDR on the underlying socket.
+  // Should be called between Open() and Bind().
   // Returns a net error code.
   int AllowAddressReuse();
 
-  // Sets corresponding flags in |socket_options_| to allow or disallow sending
-  // and receiving packets to and from broadcast addresses.
+  // Call this to allow or disallow sending and receiving packets to and from
+  // broadcast addresses.
   // Returns a net error code.
   int SetBroadcast(bool broadcast);