selftests: net: veth: make test compatible with dash

veth.sh is a shell script that uses /bin/sh; some distro (Ubuntu for
example) use dash as /bin/sh and in this case the test reports the
following error:

 # ./veth.sh: 21: local: -r: bad variable name
 # ./veth.sh: 21: local: -r: bad variable name

This happens because dash doesn't support the option "-r" with local.

Moreover, in case of missing bpf object, the script is exiting -1, that
is an illegal number for dash:

 exit: Illegal number: -1

Change the script to be compatible both with bash and dash and prevent
the errors above.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/veth.sh

@@ -18,7 +18,8 @@ ret=0
 
 cleanup() {
 	local ns
-	local -r jobs="$(jobs -p)"
+	local jobs
+	readonly jobs="$(jobs -p)"
 	[ -n "${jobs}" ] && kill -1 ${jobs} 2>/dev/null
 	rm -f $STATS
 
@@ -108,7 +109,7 @@ chk_gro() {
 
 if [ ! -f ../bpf/xdp_dummy.o ]; then
 	echo "Missing xdp_dummy helper. Build bpf selftest first"
-	exit -1
+	exit 1
 fi
 
 create_ns