wifi: nl80211: require CAP_NET_ADMIN over the target netns in SET_WIPHY_NETNS

wifi: nl80211: require CAP_NET_ADMIN over the target netns in SET_WIPHY_NETNS

NL80211_CMD_SET_WIPHY_NETNS dispatches with GENL_UNS_ADMIN_PERM, which
verifies that the caller has CAP_NET_ADMIN for the source netns. It
doesn't verify that the caller has CAP_NET_ADMIN over the target netns
selected by NL80211_ATTR_NETNS_FD or NL80211_ATTR_PID.

This diverges from the convention enforced in
net/core/rtnetlink.c::rtnl_get_net_ns_capable():

    /* For now, the caller is required to have CAP_NET_ADMIN in
     * the user namespace owning the target net ns.
     */
    if (!sk_ns_capable(sk, net->user_ns, CAP_NET_ADMIN))
        return ERR_PTR(-EACCES);

A user with CAP_NET_ADMIN in their own user namespace can therefore
push a wiphy into an arbitrary netns (including init_net) over which
they have no privilege.

Mirror the rtnetlink convention by requiring CAP_NET_ADMIN in the
target netns before calling cfg80211_switch_netns().

Signed-off-by: Maoyi Xie <maoyi.xie@ntu.edu.sg>
Link: https://patch.msgid.link/20260506064854.2207105-2-maoyixie.tju@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>