update RELEASE_NOTES and CHANGES.html for TapBridge changes

CHANGES.html

@@ -60,6 +60,10 @@ us a note on ns-developers mailing list.</p>
 <h2>Changes to build system:</h2>
 
 <h2>Changed behavior:</h2>
+<ul>
+  <li> For the TapBridge device, in UseLocal mode there is a MAC learning function. TapBridge has been waiting for the first packet received from tap interface to set the address of the bridged device to the source address of the first packet. This has caused problems with WiFi.  The new behavior is that after connection to the tap interface, ns-3 learns the MAC address of that interface with a system call and immediately sets the address of the bridged device to the learned one.  See <a href="https://www.nsnam.org/bugzilla/show_bug.cgi?id=1777">bug 1777</a> for more details.</li>
+  <li> TapBridge device now correctly implements IsLinkUp() method.</li>
+</ul>
 
 <hr>
 <h1>Changes from ns-3.18 to ns-3.18.1</h1>

RELEASE_NOTES

@@ -24,6 +24,9 @@ New user-visible features
 
 Bugs fixed
 ----------
+- Bug 1778 - Implement TapBridge::IsLinkUp() function
+- Bug 1777 - Implement the more direct way of "using" configuration of existing tap interface
+- Bug 1776 - Improve CRC performance for CsmaNetDevice in emulation modes
 
 Release 3.18.1
 ==============