Lua vlan tag value extraction

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The VLAN Display Filter Reference page lists several VLAN-related fields. You can access any of them from your Lua dissector with something like so:

-- Ref: https://www.wireshark.org/docs/wsdg_html/#wsluarm_modules
local foo = Proto("FOO", "Foo")
local foo_vlan_id = ProtoField.uint16("foo.vlan_id", "VLAN ID")

-- Section 11.2.1.1: Use Field extractor to grab field of interest
local vlan_id = Field.new("vlan.id")

function foo.dissector(tvbuf, pinfo, tree)
    local foo_tree = tree:add(foo, "Foo")
    foo_tree:add(foo_vlan_id, vlan_id().value)
end