MB-6159: Cast sasl callback func
MB-6159: Cast sasl callback func

Change-Id: Ifb8dfa1e2400aa59a4c79b04f90573165e395d86
Reviewed-on: http://review.couchbase.org/19376
Tested-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Reviewed-by: Matt Ingenthron <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@couchbase.com>

owendCB/memcached,owendCB/memcached,abhinavdangeti/memcached,daverigby/memcached,mrkwse/memcached,cloudrain21/memcached-1,couchbase/memcached,daverigby/memcached,daverigby/kv_engine,jimwwalker/memcached,abhinavdangeti/memcached,mrkwse/memcached,daverigby/memcached,cloudrain21/memcached-1,mrkwse/memcached,abhinavdangeti/memcached,daverigby/memcached,owendCB/memcached,couchbase/memcached,owendCB/memcached,daverigby/kv_engine,abhinavdangeti/memcached,mrkwse/memcached,cloudrain21/memcached-1,jimwwalker/memcached,couchbase/memcached,jimwwalker/memcached,daverigby/kv_engine,daverigby/kv_engine,cloudrain21/memcached-1,couchbase/memcached,abhinavdangeti/memcached