selftests: mptcp: connect: also cover checksum

The checksum mode has been added a while ago, but it is only validated
when manually launching mptcp_connect.sh with "-C".

The different CIs were then not validating these MPTCP Connect tests
with checksum enabled. To make sure they do, add a new test program
executing mptcp_connect.sh with the checksum mode.

Fixes: 94d66ba1d8e4 ("selftests: mptcp: enable checksum in mptcp_connect.sh")
Cc: [e-mail]
Reviewed-by: Geliang Tang <[e-mail]>
Signed-off-by: Matthieu Baerts (NGI0) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/mptcp/Makefile

···
 CFLAGS += -Wall -Wl,--no-as-needed -O2 -g -I$(top_srcdir)/usr/include $(KHDR_INCLUDES)
 
 TEST_PROGS := mptcp_connect.sh mptcp_connect_mmap.sh mptcp_connect_sendfile.sh \
-	      pm_netlink.sh mptcp_join.sh diag.sh \
+	      mptcp_connect_checksum.sh pm_netlink.sh mptcp_join.sh diag.sh \
 	      simult_flows.sh mptcp_sockopt.sh userspace_pm.sh
 
 TEST_GEN_FILES = mptcp_connect pm_nl_ctl mptcp_sockopt mptcp_inq mptcp_diag

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

···
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+MPTCP_LIB_KSFT_TEST="$(basename "${0}" .sh)" \
+	"$(dirname "${0}")/mptcp_connect.sh" -C "${@}"