Bluetooth: Controller: lll: Move packet setup after call to sw switch

lll_conn_rx_pkt_set function is called before one of radio_switch-
_complete_XXX functions calls in lll_peripheral.c. That prevents
lll_conn_rx_pkt to call any Radio setup related function that touches
NRF_RADIO->SHORTS. NRF_RADIO->SHORTS are assigned in radio_switch_-
complete_XXX functions, hence any change operation on the register done
before is overwritten.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>