Update libsrtp to upstream 1.5.0

srtp/CHANGES

 Changelog
 
+1.5.0
+ 
+  Add support for using OpenSSL crypto using the --enable-openssl 
+  option.
+
+  Add support for AES-GCM crypto suites. 
+
+  Add support for pkg_config.
+
+  Add user data API to allow user to associate additional data with a 
+  SRTP context.
+
+  This release also includes a variety of bug fixes, which can be 
+  viewed at: https://github.com/cisco/libsrtp/commits/master
+
+  Note: The change log was not maintained between versions 1.3.20 and
+        1.4.5.
+
 1.3.20
 
   Lots of changes.  Thanks to Jeff Chan for catching a memory leak and
   helping track down the endian issues with the SSRCs.
 
 1.3.8
 
   This is an interim release.  Several little-endian bugs were identified
   and fixed; this means that we can use intel/linux for development again.
 
@@ skipping 201 matching lines @@
    automatically recovers from bad estimates.  This was required to
    prevent spurious failures.
 
    Made rdbx_estimate_index(...) function smarter, so that initial RTP
    sequence numbers greater than 32,768 don't cause it to estimate the
    rollover counter of 0xffffffff.
 
 
 1.0.0   Initial release