tests/functional: Require 'user' netdev for ppc64 e500 test

When commit 72cdd672e18c extended the ppc64 e500 test to add network
support, it forgot to require the 'user' netdev backend. Fix that.

Fixes: 72cdd672e18c ("tests/functional: Replace the ppc64 e500 advent calendar test")
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250308071328.193694-1-clg@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
diff --git a/tests/functional/test_ppc64_e500.py b/tests/functional/test_ppc64_e500.py
index 9ce7ae6..f5fcad9 100755
--- a/tests/functional/test_ppc64_e500.py
+++ b/tests/functional/test_ppc64_e500.py
@@ -20,6 +20,7 @@ class E500Test(LinuxKernelTest):
 
     def test_ppc64_e500_buildroot(self):
         self.set_machine('ppce500')
+        self.require_netdev('user')
         self.cpu = 'e5500'
 
         uimage_path = self.ASSET_BR2_E5500_UIMAGE.fetch()