Add MSIX rewrite table quirk for use with VMs.

This patch solves IRQ generation problems using the mlx5en(4) driver
with xenserver v6.5.0 in SRIOV and PCI-passthrough modes.

Until further the hw.pci.msix_rewrite_table quirk must be set manually
in /boot/loader.conf .

Reviewed by: jhb @
Sponsored by: Mellanox Technologies
MFC after: 2 weeks