wifi: cfg80211: introduce cfg80211_ssid_eq()

Since SSIDs comparison is commonly used across many drivers, introduce
generic 'cfg80211_ssid_eq()' to replace driver-private implementations.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Link: https://msgid.link/20231215123859.196350-1-dmantipov@yandex.ru


[fix kernel-doc return docs]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>