wifi: cfg80211: add option for vif allowed radios

This allows users to prevent a vif from affecting radios other than the
configured ones. This can be useful in cases where e.g. an AP is running
on one radio, and triggering a scan on another radio should not disturb it.

Changing the allowed radios list for a vif is supported, but only while
it is down.

While it is possible to achieve the same by always explicitly specifying
a frequency list for scan requests and ensuring that the wrong channel/band
is never accidentally set on an unrelated interface, this change makes
multi-radio wiphy setups a lot easier to deal with for CLI users.

By itself, this patch only enforces the radio mask for scanning requests
and remain-on-channel. Follow-up changes build on this to limit configured
frequencies.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://patch.msgid.link/eefcb218780f71a1549875d149f1196486762756.1728462320.git-series.nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/uapi/linux/nl80211.h

@@ -2868,6 +2868,9 @@ enum nl80211_commands {
  *	nested item, it contains attributes defined in
  *	&enum nl80211_if_combination_attrs.
  *
+ * @NL80211_ATTR_VIF_RADIO_MASK: Bitmask of allowed radios (u32).
+ *	A value of 0 means all radios.
+ *
  * @NUM_NL80211_ATTR: total number of nl80211_attrs available
  * @NL80211_ATTR_MAX: highest attribute number currently defined
  * @__NL80211_ATTR_AFTER_LAST: internal use
@@ -3416,6 +3419,8 @@ enum nl80211_attrs {
 	NL80211_ATTR_WIPHY_RADIOS,
 	NL80211_ATTR_WIPHY_INTERFACE_COMBINATIONS,
 
+	NL80211_ATTR_VIF_RADIO_MASK,
+
 	/* add attributes here, update the policy in nl80211.c */
 
 	__NL80211_ATTR_AFTER_LAST,