selftests: drv-net: get detailed interface info

We already record output of ip link for NETIF in env for easy access.
Record the detailed version. TSO test will want to know the max tso size.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Link: https://patch.msgid.link/20250218225426.77726-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/lib/py/env.py

@@ -64,7 +64,7 @@ def __init__(self, src_path, **kwargs):
         self._ns = None
 
         if 'NETIF' in self.env:
-            self.dev = ip("link show dev " + self.env['NETIF'], json=True)[0]
+            self.dev = ip("-d link show dev " + self.env['NETIF'], json=True)[0]
         else:
             self._ns = NetdevSimDev(**kwargs)
             self.dev = self._ns.nsims[0].dev
@@ -118,7 +118,7 @@ def __init__(self, src_path, nsim_test=None):
                 raise KsftXfailEx("Test only works on netdevsim")
             self._check_env()
 
-            self.dev = ip("link show dev " + self.env['NETIF'], json=True)[0]
+            self.dev = ip("-d link show dev " + self.env['NETIF'], json=True)[0]
 
             self.v4 = self.env.get("LOCAL_V4")
             self.v6 = self.env.get("LOCAL_V6")