cfg80211: give all multi-BSSID BSS entries the same timestamp

If we just read jiffies over and over again, a non-transmitting
entry may have a newer timestamp than the transmitting one,
leading to possible confusion on expiry. Give them all the same
timestamp when creating them.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Link: https://lore.kernel.org/r/20190703133823.10530-3-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>