ice: Add stats for Rx drops at the port level

Currently we are not reporting dropped counts at the port level to
ethtool or netlink. This was found when debugging Rx dropped issues
and the total packets sent did not equal the total packets received
minus the rx_dropped, which was very confusing. To determine dropped
counts at the port level we need to read the PRTRPB_RDPC register.
To fix reporting we will store the dropped counts in the PF's
rx_discards. This will be reported to netlink by storing it in the
PF VSI's rx_missed_errors signaling that the receiver missed the
packet. Also, we will report this to ethtool in the rx_dropped.nic
field.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>