dibs: Move vlan support to dibs_dev_ops

dibs: Move vlan support to dibs_dev_ops

It can be debated how much benefit definition of vlan ids for dibs devices
brings, as the dmbs are accessible only by a single peer anyhow. But ism
provides vlan support and smcd exploits it, so move it to dibs layer as an
optional feature.

smcd_loopback simply ignores all vlan settings, do the same in
dibs_loopback.

SMC-D and ISM have a method to use the invalid VLAN ID 1FFF
(ISM_RESERVED_VLANID), to indicate that both communication peers support
routable SMC-Dv2. Tolerate it in dibs, but move it to SMC only.

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://patch.msgid.link/20250918110500.1731261-12-wintera@linux.ibm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>