implement special pipeline handling for in-band management

Reviewer: @harshsin

A new command line option is added to enable in-band management and to 
configure the VLAN to use. When a packet with this tag is received on an
uplink it will be detagged and sent to an "inband" internal port. When a
packet is sent from the inband port, it will be tagged with the configured
VLAN and sent out the first live uplink.

Also fixed a bug in the --uplink command line option, and added a missing
check to ind_ovs_uplink_first.