urlmatch: split host and port fields in `struct url_info`

urlmatch: split host and port fields in `struct url_info`

The `url_info` structure contains information about a normalized URL
with the URL's components being represented by different fields. The
host and port part though are to be accessed by the same `host` field,
so that getting the host and/or port separately becomes more involved
than really necessary.

To make the port more readily accessible, split up the host and port
fields. Namely, the `host_len` will not include the port length anymore
and a new `port_off` field has been added which includes the offset to
the port, if available.

The only user of these fields is `url_normalize_1`. This change makes it
easier later on to treat host and port differently when introducing
globs for domains.

Signed-off-by: Patrick Steinhardt <patrick.steinhardt@elego.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>