vmxnet3: Don't restart on VLAN changes

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

This re-init is unintentional for vmxnet3(4).

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