dbserver: name 0x3007 as set filter on/off, not media info

[vynulldev]

What & why

Decks send dbserver request 0x3007 before each root menu request (0x1000); a CDJ-2000NXS2 log shows it on every browse. We have handled it since the initial commit under the label "mount/media info", with no evidence behind the name.

link-spec's static analysis says otherwise. rekordbox dispatches 0x3007 to PSvDBMain::OnFilterCmd as CMD_SET_FILTER_ONOFF, the first of its five filter commands (0x3007 to 0x3407 in 0x100 steps: on/off, get property, set property, set My Tag, add My Tag item). On the deck side, XDJ-RR firmware sends it from a client wrapper named dbcl_SetFilterOnOff. So the deck turns rekordbox's browse filter on or off before opening the root menu.

• The handler is renamed to handleSetFilterOnOff, with a comment pointing at the link-spec evidence.
• Its debug log now includes the request's arguments, so the next deck session shows which state the deck asks for.
• The reply is unchanged. rekordbox's reply to 0x3007 has not been captured (link-spec only has the dispatch entry, and no conformance golden sends it), and decks accept our plain success [0x3007, 0].

Hardware testing

• Tested on: Not needed for behaviour: the reply bytes are unchanged and only the name, comment and debug log differ. A debug log from one browse on the CDJ-2000NXS2 would record the deck's arguments.

Checklist

• go build ./..., go vet ./..., and go test ./... pass
• gofmt -l . is clean
• New source files carry an SPDX header (GPL-3.0-or-later)
• Tested on real hardware (deck + firmware noted above), or this change doesn't affect deck behaviour
• I agree my contribution is licensed under the project's GPLv3