The vlan nicparam is used in openvswitch mode. This patch
exports it as VLAN environment variable so that NIC
configuration scripts can later use it.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>