selftests: mptcp: join: mute errors when ran in the background

The test is supposed to be killed before the end, which will likely
cause "Connection reset by peer" errors. It is confusing, especially
because in case of real transfer errors, the test will not be marked as
failed. But that's OK, there are many other tests checking that.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240902-net-next-mptcp-mib-mpjtx-misc-v1-9-d3e0f3773b90@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -3542,8 +3542,8 @@ userspace_tests()
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
 		set_userspace_pm $ns1
 		pm_nl_set_limits $ns2 2 2
-		speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 		wait_mpj $ns1
 		userspace_pm_add_addr $ns1 10.0.2.1 10
@@ -3575,8 +3575,8 @@ userspace_tests()
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
 		set_userspace_pm $ns2
 		pm_nl_set_limits $ns1 0 1
-		speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 		wait_mpj $ns2
 		userspace_pm_add_sf $ns2 10.0.3.2 20
@@ -3603,8 +3603,8 @@ userspace_tests()
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
 		set_userspace_pm $ns2
 		pm_nl_set_limits $ns1 0 1
-		speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 		wait_mpj $ns2
 		chk_mptcp_info subflows 0 subflows 0
@@ -3624,8 +3624,8 @@ userspace_tests()
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
 		set_userspace_pm $ns2
 		pm_nl_set_limits $ns1 0 1
-		speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 		wait_mpj $ns2
 		userspace_pm_add_sf $ns2 10.0.3.2 20
@@ -3648,8 +3648,8 @@ userspace_tests()
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
 		set_userspace_pm $ns1
 		pm_nl_set_limits $ns2 1 1
-		speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 		wait_mpj $ns1
 		userspace_pm_add_addr $ns1 10.0.2.1 10
@@ -3679,8 +3679,8 @@ endpoint_tests()
 		pm_nl_set_limits $ns1 2 2
 		pm_nl_set_limits $ns2 2 2
 		pm_nl_add_endpoint $ns1 10.0.2.1 flags signal
-		speed=slow \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ speed=slow \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 
 		wait_mpj $ns1
@@ -3706,8 +3706,8 @@ endpoint_tests()
 		pm_nl_set_limits $ns2 0 3
 		pm_nl_add_endpoint $ns2 10.0.1.2 id 1 dev ns2eth1 flags subflow
 		pm_nl_add_endpoint $ns2 10.0.2.2 id 2 dev ns2eth2 flags subflow
-		test_linkfail=4 speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ test_linkfail=4 speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 
 		wait_mpj $ns2
@@ -3783,8 +3783,8 @@ endpoint_tests()
 		# broadcast IP: no packet for this address will be received on ns1
 		pm_nl_add_endpoint $ns1 224.0.0.1 id 2 flags signal
 		pm_nl_add_endpoint $ns1 10.0.1.1 id 42 flags signal
-		test_linkfail=4 speed=5 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ test_linkfail=4 speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 
 		wait_mpj $ns2
@@ -3856,8 +3856,8 @@ endpoint_tests()
 		# broadcast IP: no packet for this address will be received on ns1
 		pm_nl_add_endpoint $ns1 224.0.0.1 id 2 flags signal
 		pm_nl_add_endpoint $ns2 10.0.3.2 id 3 flags subflow
-		test_linkfail=4 speed=20 \
-			run_tests $ns1 $ns2 10.0.1.1 &
+		{ test_linkfail=4 speed=20 \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
 		local tests_pid=$!
 
 		wait_attempt_fail $ns2