Support link aggregation

[henn]

For the purposes of higher availability in the case of port failure as well as higher bandwidth, it would be great for HaaS to support link aggregation, which allows 2 or more ports to be combined into a single Link Aggregation Group (LAG).

Many times, to save money in terms of cables, server ports and network ports, only a couple of cables are connected from servers to the network switches. Supporting LAGs, especially when combined with 802.1q tagging(see #278), would mean that even in these constrained environments, several VLANs could be supported to nodes with higher reliability and performance.