mt76: mt7915: add partial add_bss_info command on testmode init

This is a preliminary patch for DBDC and ipg config support
in testmode.

The wmm_idx of band1 should be configured by this command to
make band1 Tx work normally. Also, for setting ipg, FW needs a
non-empty bss_info structure to do edca parameters update.

Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Acked-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>