shared.cfg.guest-hw: Move ethtool's config to its own config file

The config variants in guest-hw.cfg file would overwite config
in the test case, thus let's put them all in test's config file
directly.

CC: Yunping Zheng <yunzheng@redhat.com>
Signed-off-by: NQingtang Zhou <qzhou@redhat.com>

tests/cfg/ethtool.cfg

 - ethtool:
     virt_test_type = qemu libvirt
     only Linux
-    no rtl8139
-    no RHEL.3.9
+    only e1000, virtio_net
+    no RHEL.3
     type = ethtool
     filesize = 512
     nic_mode = tap
-    supported_features = "tx rx sg tso"
-    RHEL.4:
-        e1000:
-            supported_features = "tx rx sg tso"
-        virtio_net:
-            supported_features = "tx sg tso"
-    RHEL.5:
     e1000:
-            supported_features = "tx rx sg tso gso"
-        virtio_net:
-            supported_features = "tx sg tso gso"
-    RHEL.6:
         # gso gro lro is only supported by latest kernel
-        e1000:
         supported_features = "tx rx sg tso gso gro lro"
     virtio_net:
         supported_features = "tx sg tso gso"
+    RHEL.4..e1000:
+        supported_features = "tx rx sg tso"
+    RHEL.4..virtio_net:
+        supported_features = "tx sg tso"
+    RHEL.5..e1000:
+        supported_features = "tx rx sg tso gso"