selftests: cmsg_ipv6: repeat the exact packet

BugLink: https://bugs.launchpad.net/bugs/2059991

[ Upstream commit 4b00d0c ]

cmsg_ipv6 test requests tcpdump to capture 4 packets,
and sends until tcpdump quits. Only the first packet
is "real", however, and the rest are basic UDP packets.
So if tcpdump doesn't start in time it will miss
the real packet and only capture the UDP ones.

This makes the test fail on slow machine (no KVM or with
debug enabled) 100% of the time, while it passes in fast
environments.

Repeat the "real" / expected packet.

Fixes: 9657ad0 ("selftests: net: test IPV6_TCLASS")
Fixes: 05ae83d ("selftests: net: test IPV6_HOPLIMIT")
Signed-off-by: Jakub Kicinski <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Portia Stephens <[email protected]>
Signed-off-by: Roxana Nicolescu <[email protected]>

Author: kuba-moo

tools/testing/selftests/net/cmsg_ipv6.sh

@@ -91,7 +91,7 @@ for ovr in setsock cmsg both diff; do
 	check_result $? 0 "TCLASS $prot $ovr - pass"
 
 	while [ -d /proc/$BG ]; do
-	    $NSEXE ./cmsg_sender -6 -p u $TGT6 1234
+	    $NSEXE ./cmsg_sender -6 -p $p $m $((TOS2)) $TGT6 1234
 	done
 
 	tcpdump -r $TMPF -v 2>&1 | grep "class $TOS2" >> /dev/null
@@ -128,7 +128,7 @@ for ovr in setsock cmsg both diff; do
 	check_result $? 0 "HOPLIMIT $prot $ovr - pass"
 
 	while [ -d /proc/$BG ]; do
-	    $NSEXE ./cmsg_sender -6 -p u $TGT6 1234
+	    $NSEXE ./cmsg_sender -6 -p $p $m $LIM $TGT6 1234
 	done
 
 	tcpdump -r $TMPF -v 2>&1 | grep "hlim $LIM[^0-9]" >> /dev/null