BUG/MEDIUM: server/cli: unlock server lock on failure in cli_parse_set_server

BUG/MEDIUM: server/cli: unlock server lock on failure in cli_parse_set_server

In cli_parse_set_server()'s 'ssl' branch, the server lock is taken,
and not released in case srv_set_ssl() fails, resulting in a dead lock
and a panic the next time an attempt to touch this server is made. The
lock must be released on all error paths.

This was introduced in 3.3 by commit f8f94ffc9 ("BUG/MEDIUM: server:
Use sni as pool connection name for SSL server only") which was marked
for backporting to 3.0, so this must likely be backported that far.