selftests: udpgso_bench.sh explicitly requires bash

The udpgso_bench.sh script requires several bash-only features. This
may cause random failures if the default shell is not bash.
Address the above explicitly requiring bash as the script interpreter

Fixes: 3a687bef14 ("selftests: udp gso benchmark")
Signed-off-by: Paolo Abeni <[email protected]>
Acked-by: Willem de Bruijn <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

tools/testing/selftests/net/udpgso_bench.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 # SPDX-License-Identifier: GPL-2.0
 #
 # Run a series of udpgso benchmarks