wifi: mac80211: mesh: reset the CSA state when leaving

In the Linux kernel, the following vulnerability has been resolved: wifi: mac80211: mesh: reset the CSA state when leaving ifmsh->csa is allocated in ieee80211_mesh_csa_beacon() and only freed in ieee80211_mesh_finish_csa(), i.e. when the channel switch completes. Leaving the mesh while a switch is still pending therefore leaks it. Additionally, ifmsh->csa_role and ifmsh->chsw_ttl have their state leak in this case, so things can get mixed up in addition to the memory leak. Refactor the reset and call it in ieee80211_stop_mesh() to fix it all.

Where it's fixed