selftests: pmtu: properly redirect stderr to /dev/null

The cleanup function uses "$CMD 2 > /dev/null", which doesn't actually
send stderr to /dev/null, so when the netns doesn't exist, the error
message is shown. Use "2> /dev/null" instead, so that those messages
disappear, as was intended.

Fixes: d1f1b9cbf34c ("selftests: net: Introduce first PMTU test")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/pmtu.sh

@@ -178,8 +178,8 @@ setup() {
 
 cleanup() {
 	[ ${cleanup_done} -eq 1 ] && return
-	ip netns del ${NS_A} 2 > /dev/null
-	ip netns del ${NS_B} 2 > /dev/null
+	ip netns del ${NS_A} 2> /dev/null
+	ip netns del ${NS_B} 2> /dev/null
 	cleanup_done=1
 }