e1000: fix igb VF stats

igb VF must not read normal stat registers and only read a limited
set of registers. The PF registers also don't make since as the VF
is an internal port, and there is no PHY to collect stats like CRC
errors from.

PR: 282309
Obtained from: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D52326