Fix an issue with res_http_websocket where the chan_sip WebSocket handler could not be registered.

On some systems the optional API support uses the GCC compiler attribute "weakref" to provide its
functionality. This code changes the function names and prefixes "__" to the front. The
res_http_websocket exports file did not take this into account, thereby not allowing those functions
to be global and ultimately found.

(closes issue ASTERISK-20631)
Reported by: danjenkins
........

Merged revisions 375559 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@375560 65c4cc65-6c06-0410-ace0-fbb531ad65f3