modules.lxc: don't clobber lxc.network.type setting

This fixes a regression which causes the network type specified in the lxc profile to be overwritten.

@kiorky, is this going to break anything for you?
This fix is not correct i think.
If i input a new type it must be applied.
What's in your case the value of "otype", and "ntype" ?
I tihking of another fix if i understood well the problem.