LinuxKPI: 802.11: remove special handling for (*ic_scan_curchan)

Remove the originally disabling of (*ic_scan_curchan), which for iwlwifi
was not needed. The condition always only was approximate.

A set IEEE80211_FEXT_SCAN_OFFLOAD will still prevent net80211 from sending
probe_reqs if handled by driver/firmware.
ic_scan_curchan will re-arm the timer to switch channels for drivers which
need it (e.g., rtw88, but that again is a NOP for iwlwifi).

So enabling ic_scan_curchan should not have further side effects for iwlwifi
but allow other drivers to work better.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days