libnetwork/netavark: simplify isMacVlan init

This fixes the following staticcheck warning:

> libnetwork/netavark/config.go:297:2: QF1007: could merge conditional assignment into variable declaration (staticcheck)
> 	isMacVlan := true
> 	^

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

common/libnetwork/netavark/config.go

@@ -294,10 +294,7 @@ func createIpvlanOrMacvlan(network *types.Network) error {
 	}
 
 	driver := network.Driver
-	isMacVlan := true
-	if driver == types.IPVLANNetworkDriver {
-		isMacVlan = false
-	}
+	isMacVlan := driver != types.IPVLANNetworkDriver
 
 	// always turn dns off with macvlan, it is not implemented in netavark
 	// and makes little sense to support with macvlan