MEDIUM: config: make str2listener() use str2sa_range() to parse unix addresses

MEDIUM: config: make str2listener() use str2sa_range() to parse unix addresses

Now that str2sa_range() knows how to parse UNIX addresses, make str2listener()
use it. It simplifies the function. Next step consists in unifying the error
handling to further simplify the call.

Tests have been done and show that unix sockets are correctly handled, with
and without prefixes, both for global stats and normal "bind" statements.