order switch to facilitate jump-table
libwebsockets_read: cleanup + only return 0 from http_complete if connection is keep-alive.

Remaining:
 - double-check lws_allocate_header_table is matched with cleanup in all cases
 - make sure repeat requests don't stomp on each other's memory.
If LWS_CALLBACK_HTTP returns 0, we're not issuing a file, we're not parsing a body, and the connection type is keep-alive: set connmode to HTTP_SERVING and reallocate header table.