selftests: udpgro: no need to load xdp for gro

After commit d7db7775 ("net: veth: do not manipulate GRO when using
XDP"), there is no need to load XDP program to enable GRO. On the other
hand, the current test is failed due to loading the XDP program. e.g.

 # selftests: net: udpgro.sh
 # ipv4
 #  no GRO              ok
 #  no GRO chk cmsg     ok
 #  GRO                 ./udpgso_bench_rx: recv: bad packet len, got 1472, expected 14720
 #
 # failed

 [...]

 #  bad GRO lookup      ok
 #  multiple GRO socks  ./udpgso_bench_rx: recv: bad packet len, got 1452, expected 14520
 #
 # ./udpgso_bench_rx: recv: bad packet len, got 1452, expected 14520
 #
 # failed
 ok 1 selftests: net: udpgro.sh

After fix, all the test passed.

 # ./udpgro.sh
 ipv4
  no GRO                                  ok
  [...]
  multiple GRO socks                      ok

Fixes: d7db7775 ("net: veth: do not manipulate GRO when using XDP")
Reported-by: Yi Chen <yiche@redhat.com>
Closes: https://issues.redhat.com/browse/RHEL-53858


Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>