iavf: Add explicit ifdi_needs_reset for VLAN changes

In rS360398, a new iflib device method was added with default of opt out
for VLAN events needing an interface reset.

iavf(4) was the original need for this, because VLAN filter changes
currently have negative interactions with Malicious Driver Detection.

Add iavf_if_needs_restart and explicitly enable VLAN re-init.

MFC after: 2 weeks
Sponsored by: BBOX.io
Differential Revision: https://reviews.freebsd.org/D41558