iwlwifi: pass context to iwl_send_rxon_timing

Sometimes we need to send RXON timing even
when we don't have a virtual interface yet,
so pass the context and allow passing one
without a virtual interface pointer.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>