wifi: cfg80211: add cfg80211_stop_link() for per-link teardown

wifi: cfg80211: add cfg80211_stop_link() for per-link teardown

Currently, whenever cfg80211_stop_iface() is called, the entire iface
is stopped. However, there could be a need in AP/P2P_GO mode, where
one would like to stop a single link in MLO operation instead of the
whole MLD interface.

Hence, introduce cfg80211_stop_link() to allow drivers to tear down
only a specified AP/P2P_GO link during MLO operation. Passing -1
preserves the existing behavior of stopping the whole interface. Make
cfg80211_stop_iface() call this function by passing -1 to keep the
default behavior the same, that is, to stop all links and use
cfg80211_stop_link() with the desired link_id for AP/P2P_GO mode, to
stop only that link.

This brings no behavioral change for single-link/non-MLO interfaces,
and enables drivers to stop an AP/P2P_GO link without disrupting other
links on the same interface.

Signed-off-by: Manish Dharanenthiran <manish.dharanenthiran@oss.qualcomm.com>
Link: https://patch.msgid.link/20251127-stop_link-v2-1-43745846c5fd@qti.qualcomm.com
[make cfg80211_stop_iface() inline]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>