net: bridge: vlan options: add support for tunnel id dumping

Add a new option - BRIDGE_VLANDB_ENTRY_TUNNEL_ID which is used to dump
the tunnel id mapping. Since they're unique per vlan they can enter a
vlan range if they're consecutive, thus we can calculate the tunnel id
range map simply as: vlan range end id - vlan range start id. The
starting point is the tunnel id in BRIDGE_VLANDB_ENTRY_TUNNEL_ID. This
is similar to how the tunnel entries can be created in a range via the
old API (a vlan range maps to a tunnel range).

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