Include additional LLDP fields in liblldp

Currently the liblldp used in the openflowplugin does not support a few fields from the LLDP spec.

The following 

• system-description,
• port-description,
• system-capabilities,
• management-address

This story to include support for these fields in the library so that any downstream applications can extract these from an incoming LLDP packet.

Note: Although these fields are not present in the controller generated packets, it is useful when capturing any external LLDP packets on host ports.

Avishnoi