qcacld-3.0: Fix invalid timestamp in kernel bss entry

Driver report beacon/probe rsp frame in wlan_hdd_inform_bss_frame
to kernel. "boottime_ns" field needs be filled by "scansystimensec"
in nanosecond, so assign "boottime_ns" (NS) from scan entry to
bss_description instead of "scan_entry_time" (MS).

Change-Id: Id22f119f41f8cf60a8aadc9e04c4f18424c88413
CRs-Fixed: 2870827