util: skip RDMA detection for non-PCI network devices

Only PCI devices have '/sys/class/net/<ifname>/device/resource' so we
need to skip this check for all other network devices.

Without this patch and RDMA enabled libvirt will not detect any network
device that doesn't have the path above which includes 'lo', 'virbr',
'tun', etc.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1639258Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

src/util/virnetdev.c

@@ -2914,8 +2914,14 @@ virNetDevRDMAFeature(const char *ifname,
 
     if (virAsprintf(&eth_devpath, SYSFS_NET_DIR "%s/device/resource", ifname) < 0)
         goto cleanup;
-    if (!virFileExists(eth_devpath))
+
+    /* If /sys/class/net/<ifname>/device/resource doesn't exist it is not a PCI
+     * device and therefore it will not have RDMA. */
+    if (!virFileExists(eth_devpath)) {
+        ret = 0;
         goto cleanup;
+    }
+
     if (virFileReadAll(eth_devpath, RESOURCE_FILE_LEN, &eth_res_buf) < 0)
         goto cleanup;