[iwm] Sync valid_tx_ant and valid_rx_ant mask handling with iwlwifi.
- This fixes the phy_cfg field sent in the iwm_send_phy_cfg_cmd() command, which wasn't taking into account the valid_rx_ant and valid_tx_ant masks from nvm_data before.
Tested:
- 7260, STA mode, 2G and 5G
Obtained from: DragonflyBSD commit cbb82693c18fd71b4eb86855b82d03995f352d65