ixl(4): Use GL_RXERR1 register for correct oversize packet count

The driver sets the Maximum Transmission Unit (MTU) at the Virtual Station
Interface (VSI) level, which leads to a discrepancy in the GLPRT_ROC counter's
ability to accurately tally oversized packets, as this counter operates at the
physical port level. To rectify this issue, it is necessary to take an
additional register (GL_RXERR1) into account to obtain the correct count of
oversized packets.

Signed-off-by: Yogesh Bhosale <yogesh.bhosale@intel.com>
Signed-off-by: Eric Joyner <erj@FreeBSD.org>

Reviewed by: erj@
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D45870