qemu: eliminate memory leak in qemuDomainUpdateDeviceConfig

This function was freeing a virDomainNetDef with
VIR_FREE(). virDomainNetDef is a complex structure with many pointers
to other dynamically allocated data; to properly free it
virDomainNetDefFree() must be called instead, otherwise several
strings (and potentially other things) will be leaked.

src/qemu/qemu_driver.c

@@ -5570,7 +5570,7 @@ qemuDomainUpdateDeviceConfig(virDomainDefPtr vmdef,
             return -1;
         }
 
-        VIR_FREE(vmdef->nets[pos]);
+        virDomainNetDefFree(vmdef->nets[pos]);
 
         vmdef->nets[pos] = net;
         dev->data.net = NULL;