selftests: net: tsn_lib: create common helper for counting received packets

This snippet will be necessary for a future isochron-based test, so
provide a simpler high-level interface for counting the received
packets.

Signed-off-by: Vladimir Oltean <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/drivers/net/ocelot/psfp.sh

···
 		"" \
 		"${isochron_dat}"
 
-	# Count all received packets by looking at the non-zero RX timestamps
-	received=$(isochron report \
-		--input-file "${isochron_dat}" \
-		--printf-format "%u\n" --printf-args "R" | \
-		grep -w -v '0' | wc -l)
-
+	received=$(isochron_report_num_received "${isochron_dat}")
 	if [ "${received}" = "${expected}" ]; then
 		RET=0
 	else

tools/testing/selftests/net/forwarding/tsn_lib.sh

···
 
 	cpufreq_restore ${ISOCHRON_CPU}
 }
+
+isochron_report_num_received()
+{
+	local isochron_dat=$1; shift
+
+	# Count all received packets by looking at the non-zero RX timestamps
+	isochron report \
+		--input-file "${isochron_dat}" \
+		--printf-format "%u\n" --printf-args "R" | \
+		grep -w -v '0' | wc -l
+}