lxd/db/network: Provide way to identifty unknown network type in getNetwork
lxd/db/network: Provide way to identifty unknown network type in getNetwork

Don't silently convert to bridge. Existing networks will get the default type ID of 0, so will be recognised as bridge correctly.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,Skarlso/lxd,lxc/lxd,atxwebs/lxd,hallyn/lxd,mjeanson/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,mjeanson/lxd,Skarlso/lxd,stgraber/lxd,mjeanson/lxd,Skarlso/lxd,Skarlso/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd