network: create separate config object for virNetworkDriverState

network: create separate config object for virNetworkDriverState

Similar to the other drivers, virNetworkDriverState now has a
virObject-derived object called virNetworkDriverConfig which is used
for config items.

As a starting point, the directory paths used by the network driver
are moved there (again, parallelling what is done for other drivers).

Using items in virNetworkDriverConfig is (yes, again) similar to using
items in the other drivers' config - anything in the config object is
immutable (once initialized), so the state object only needs to be
locked while getting a reference to the config object, and then the
members of the config object can be safely used until the config
object is unrefed.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>