Disabled the use of flowid for lagg by default

Disabled the use of RSS hash from the network card aka flowid for
lagg(4) interfaces by default as it's currently incompatible with
the lacp and loadbalance protocols.

The incompatibility is due to the fact that the flowid isn't know
for the first packet of a new outbound stream which can result in
the hash calculation method changing and hence a stream being
incorrectly split across multiple interfaces during normal
operation.

This can be re-enabled by setting the following in loader.conf:
net.link.lagg.default_use_flowid="1"

Discussed with: kmacy
Sponsored by: Multiplay