res_http_websocket: Export symbol for ast_websocket_set_timeout

Thanks to Sean Bright for pointing out that this was missed in #asterisk-dev.
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Merged revisions 417419 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 417420 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@417421 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_http_websocket.exports.in

 {
 	global:
 		LINKER_SYMBOL_PREFIX*ast_websocket_*;
+		LINKER_SYMBOL_PREFIX*ast_websocket_set_timeout;
 	local:
 		*;
 };