wifi: mt76: mt7915: do not check state before configuring implicit beamform

Do not need to check running state before configuring implicit Tx
beamform. It is okay to configure implicit Tx beamform in run time.
Noted that the existing connected stations will be applied for new
configuration only if they reconnected to the interface.

Fixes: 6d6dc980 ("mt76: mt7915: add implicit Tx beamforming support")
Signed-off-by: Howard Hsu <howard-yh.hsu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>