This patch adds support for manipulating vlan/tunnel mappings. The
tunnel ids are globally unique and are one per-vlan. There were two
trickier issues - first in order to support vlan ranges we have to
compute the current tunnel id in the following way:
 - base tunnel id (attr) + current vlan id - starting vlan id
This is in line how the old API does vlan/tunnel mapping with ranges. We
already have the vlan range present, so it's redundant to add another
attribute for the tunnel range end. It's simply base tunnel id + vlan
range. And second to support removing mappings we need an out-of-band way
to tell the option manipulating function because there are no
special/reserved tunnel id values, so we use a vlan flag to denote the
operation is tunnel mapping removal.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>