upload-pack: rename `enum` to reflect the operation

upload-pack: rename `enum` to reflect the operation

While 3145ea957d (upload-pack: introduce fetch server command,
2018-03-15) added support for the `fetch` command, from the server's
point of view it is an upload, and hence the `enum` should really be
called `upload_state` instead of `fetch_state`. Likewise, rename its
values.

This also helps unconfuse CodeQL which would otherwise be at sixes or
sevens about having _two_ non-local definitions of the same `enum` with
the same values.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>