iwlwifi: rename TX_CMD_FLG_BT_DIS_MSK

The flag name is a little misleading, this
flag instructs the device to ignore bluetooth
messages for purposes of frame transmissions,
so rename the flag to TX_CMD_FLG_IGNORE_BT.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>