net/fm10k/base: improve VF multi-bit VLAN update requests

net/fm10k/base: improve VF multi-bit VLAN update requests

The VF uses a multi-bit update request to clear unused VLANs whenever it
resets. However, an accident in a previous refactor broke multi-bit
updates for VFs, due to misreading a comment in fm10k_vf.c and
attempting to reduce code duplication. The problem occurs because
a multi-bit request has a non-zero length, and the PF would simply drop
any request with the upper 16 bits set. In addition, a multi-bit vlan
update does not have a concept for "VLAN 0" as the single bit update
does.

A previous revision of this patch resolved the issue by simply removing
the upper 16 bit check and the iov_select_vid checks. However, this would
remove the checks for default VID and for ensuring no other VLANs can be
enabled except pf_vid when it has been set. To resolve that issue, this
revision uses the iov_select_vid when we have a single-bit update, and
denies any multi-bit update when the VLAN was administratively set by
the PF. This should be ok since the PF properly updates VLAN_TABLE when
it assigns the PF vid. This ensures that requests to add or "remove" the
PF vid work as expected, but a rogue VF could not use the multi-bit
update as a loophole to attempt receiving traffic on other VLANs.

Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>