selftests: mptcp: join: simplify checksum_tests

The four checksum tests are similar, only one line is different. So
a for-loop can be used to simplify these tests.
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240902-net-next-mptcp-mib-mpjtx-misc-v1-10-d3e0f3773b90@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -363,7 +363,7 @@ reset_with_checksum()
 	local ns1_enable=$1
 	local ns2_enable=$2
 
-	reset "checksum test ${1} ${2}" || return 1
+	reset "checksum test ${ns1_enable} ${ns2_enable}" || return 1
 
 	ip netns exec $ns1 sysctl -q net.mptcp.checksum_enabled=$ns1_enable
 	ip netns exec $ns2 sysctl -q net.mptcp.checksum_enabled=$ns2_enable
@@ -3032,37 +3032,16 @@ syncookies_tests()
 
 checksum_tests()
 {
-	# checksum test 0 0
-	if reset_with_checksum 0 0; then
-		pm_nl_set_limits $ns1 0 1
-		pm_nl_set_limits $ns2 0 1
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 0 0 0
-	fi
-
-	# checksum test 1 1
-	if reset_with_checksum 1 1; then
-		pm_nl_set_limits $ns1 0 1
-		pm_nl_set_limits $ns2 0 1
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 0 0 0
-	fi
-
-	# checksum test 0 1
-	if reset_with_checksum 0 1; then
-		pm_nl_set_limits $ns1 0 1
-		pm_nl_set_limits $ns2 0 1
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 0 0 0
-	fi
-
-	# checksum test 1 0
-	if reset_with_checksum 1 0; then
-		pm_nl_set_limits $ns1 0 1
-		pm_nl_set_limits $ns2 0 1
-		run_tests $ns1 $ns2 10.0.1.1
-		chk_join_nr 0 0 0
-	fi
+	local checksum_enable
+	for checksum_enable in "0 0" "1 1" "0 1" "1 0"; do
+		# checksum test 0 0, 1 1, 0 1, 1 0
+		if reset_with_checksum ${checksum_enable}; then
+			pm_nl_set_limits $ns1 0 1
+			pm_nl_set_limits $ns2 0 1
+			run_tests $ns1 $ns2 10.0.1.1
+			chk_join_nr 0 0 0
+		fi
+	done
 }
 
 deny_join_id0_tests()