nimble/host/sm: check for SC in ble_sm_pair_req_rx if BLE_SM_SC_ONLY
nimble/host/sm: check for SC in ble_sm_pair_req_rx if BLE_SM_SC_ONLY

For BLE_SM_SC_ONLY mode it's mandatory to use SC.

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble