KEEPALIVE_MECHANISM_CONCHECK was added but can't be enabled

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#### Description <!-- Describe your changes in detail --> add case for KEEPALIVE_MECHANISM_CONCHECK in mod_init validation of ws_keepalive_mechanism You can view, comment on, or merge this pull request online at:

https://github.com/kamailio/kamailio/pull/2966

-- Commit Summary --

* websockets: enable KEEPALIVE_MECHANISM_CONCHECK

-- File Changes --

M src/modules/websocket/websocket.c (1)

-- Patch Links --

https://github.com/kamailio/kamailio/pull/2966.patch https://github.com/kamailio/kamailio/pull/2966.diff