em/ix/ixv/ixl/iavf: Implement ifdi_needs_restart iflib method

Pursuant to r360398, implement driver-specific versions of the
ifdi_needs_restart iflib device method.

Some (if not most?) Intel network cards don't need reinitializing when a
VLAN is added or removed from the device hardware, so these implement
ifdi_needs_restart in a way that tell iflib not to bring the interface
up or down when a VLAN is added or removed, regardless of whether the
VLAN_HWFILTER interface capability flag is set or not.

This could potentially solve several PRs relating to link flaps that
occur when VLANs are added/removed to devices.

Signed-off-by: Eric Joyner <erj@freebsd.org>

PR: 240818, 241785
Reviewed by: gallatin@, olivier@
MFC after: 3 days
MFC with: r360398
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D24659