selftests: mptcp: add csum mib check for mptcp_connect

This patch added the data checksum error mib counters check for the
script mptcp_connect.sh when the data checksum is enabled.

In do_transfer(), got the mib counters twice, before and after running
the mptcp_connect commands. The latter minus the former is the actual
number of the data checksum mib counter.

The output looks like this:

ns1 MPTCP -> ns2 (dead:beef:1::2:10007) MPTCP   (duration    86ms) [ OK ]
ns1 MPTCP -> ns2 (10.0.2.1:10008      ) MPTCP   (duration    66ms) [ FAIL ]
server got 1 data checksum error[s]

Fixes: 94d66ba1 ("selftests: mptcp: enable checksum in mptcp_connect.sh")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/255Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -432,6 +432,8 @@ do_transfer()
 	local stat_ackrx_last_l=$(get_mib_counter "${listener_ns}" "MPTcpExtMPCapableACKRX")
 	local stat_cookietx_last=$(get_mib_counter "${listener_ns}" "TcpExtSyncookiesSent")
 	local stat_cookierx_last=$(get_mib_counter "${listener_ns}" "TcpExtSyncookiesRecv")
+	local stat_csum_err_s=$(get_mib_counter "${listener_ns}" "MPTcpExtDataCsumErr")
+	local stat_csum_err_c=$(get_mib_counter "${connector_ns}" "MPTcpExtDataCsumErr")
 
 	timeout ${timeout_test} \
 		ip netns exec ${listener_ns} \
@@ -524,6 +526,23 @@ do_transfer()
 		fi
 	fi
 
+	if $checksum; then
+		local csum_err_s=$(get_mib_counter "${listener_ns}" "MPTcpExtDataCsumErr")
+		local csum_err_c=$(get_mib_counter "${connector_ns}" "MPTcpExtDataCsumErr")
+
+		local csum_err_s_nr=$((csum_err_s - stat_csum_err_s))
+		if [ $csum_err_s_nr -gt 0 ]; then
+			printf "[ FAIL ]\nserver got $csum_err_s_nr data checksum error[s]"
+			rets=1
+		fi
+
+		local csum_err_c_nr=$((csum_err_c - stat_csum_err_c))
+		if [ $csum_err_c_nr -gt 0 ]; then
+			printf "[ FAIL ]\nclient got $csum_err_c_nr data checksum error[s]"
+			retc=1
+		fi
+	fi
+
 	if [ $retc -eq 0 ] && [ $rets -eq 0 ]; then
 		printf "[ OK ]"
 	fi