Fix externalhmac.h/.cc to compile with libsrtp 1 and 2

Fix externalhmac.h/.cc to compile with libsrtp 1 and 2

This was missed in the first pass because this code only compiles in
Chromium.

BUG=webrtc:6376
Committed: https://crrev.com/8cab52db489b14552d6044232c215ab0420db4fc
Cr-Commit-Position: refs/heads/master@{#14591}

[mattdr-at-webrtc.org, 2016-10-10 03:52:39]

mattdr@webrtc.org changed reviewers:
+ deadbeef@webrtc.org

[mattdr-at-webrtc.org, 2016-10-10 03:52:40]

I verified this by changing the WebRTC build to bring in these two files and to
define ENABLE_EXTERNAL_AUTH. The resulting code compiled with libsrtp1 and
libsrtp2.

[Taylor Brandstetter, 2016-10-10 19:34:11]

lgtm

[mattdr-at-webrtc.org, 2016-10-10 22:03:09]

The CQ bit was checked by mattdr@webrtc.org

[commit-bot: I haz the power, 2016-10-10 22:03:16]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2016-10-10 22:33:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-10 22:33:46]

Description was changed from

==========
Fix externalhmac.h/.cc to compile with libsrtp 1 and 2

This was missed in the first pass because this code only compiles in
Chromium.

BUG=webrtc:6376
==========

to

==========
Fix externalhmac.h/.cc to compile with libsrtp 1 and 2

This was missed in the first pass because this code only compiles in
Chromium.

BUG=webrtc:6376

Committed: https://crrev.com/8cab52db489b14552d6044232c215ab0420db4fc
Cr-Commit-Position: refs/heads/master@{#14591}
==========

[commit-bot: I haz the power, 2016-10-10 22:33:47]

Patchset 1 (id:??) landed as
https://crrev.com/8cab52db489b14552d6044232c215ab0420db4fc
Cr-Commit-Position: refs/heads/master@{#14591}