Fix pmtu.sh result checking in ubuntu_kernel_selftests

[Po-Hsu Lin]

[Impact]
In pmtu.sh test from ubuntu_kernel_selftests, there is a syntax issue for test result checking which will make it always report pass if the last test in the script has passed.

[Fix]
* 63e201916b selftests: pmtu.sh: fix result checking

[Test Plan]
Run the patched pmtu.sh from kernel tree. Also apply the following patch to validate this fix:

diff --git a/tools/testing/selftests/net/pmtu.sh b/tools/testing/selftests/net/pmtu.sh
index f838dd3..cb62a75 100755
--- a/tools/testing/selftests/net/pmtu.sh
+++ b/tools/testing/selftests/net/pmtu.sh
@@ -266,7 +266,9 @@ tests="
        list_flush_ipv4_exception ipv4: list and flush cached exceptions 1
        list_flush_ipv6_exception ipv6: list and flush cached exceptions 1
        pmtu_ipv4_route_change ipv4: PMTU exception w/route replace 1
- pmtu_ipv6_route_change ipv6: PMTU exception w/route replace 1"
+ pmtu_ipv6_route_change ipv6: PMTU exception w/route replace 1
+ emit_fail Test that will emit fail result 0
+ emit_pass Test that will emit pass result 0"

 NS_A="ns-A"
 NS_B="ns-B"
@@ -2232,6 +2234,13 @@ test_pmtu_ipv6_route_change() {
        test_pmtu_ipvX_route_change 6
 }

+test_emit_fail() {
+ false
+}
+test_emit_pass() {
+ true
+}
+
 usage() {
        echo
        echo "$0 [OPTIONS] [TEST]..."

Check the return value of this script, it should be 1

[Regression Potential]
This is just changing test result processing behaviour, no actual impact to any kernel function. But we might see new failure discovered by this test.

[Po-Hsu Lin (cypressyew)]

This has landed via stable update bug 2049432 since Ubuntu-5.15.0-96.106