MEDIUM: stats: make use of the standard "bind" parsers to parse global socket

MEDIUM: stats: make use of the standard "bind" parsers to parse global socket

The global stats socket statement now makes use of the standard bind parsers.
This results in all UNIX socket options being set by proto_uxst and in all
TCP and SSL options being inherited and usable. For example it is now possible
to enable a stats socket over SSL/TCP by appending the "ssl" keyword and a
certificate after "crt".

The code is simplified since we don't have a special case to parse this config
keyword anymore.