network: warn about unknown sections when parsing .netdev files

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1774242.
Now we'll emit the warning about unknown section [Netdev], making the issue
much easier to diagnose.

src/network/netdev/netdevsim.c

@@ -4,7 +4,7 @@
 
 const NetDevVTable netdevsim_vtable = {
         .object_size = sizeof(NetDevSim),
-        .sections = "Match\0NetDev\0",
+        .sections = NETDEV_COMMON_SECTIONS,
         .create_type = NETDEV_CREATE_INDEPENDENT,
         .generate_mac = true,
 };