ice: Use ICE_RLAN_BASE_S instead of magic number

Commit 72adf242 ("ice: Move common functions out of ice_main.c part
2/7") moved an older version of ice_setup_rx_ctx() function with
usage of magic number 7.
Reimplement the commit 5ab52244

 ("ice: Cleanup magic number") to use
ICE_RLAN_BASE_S instead of magic number.

Signed-off-by: Anatolii Gerasymenko <anatolii.gerasymenko@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>