selftests: vrf_route_leaking: remove ipv6_ping_frag from default testing

As the initial commit 1a017276 ("selftests: Add VRF route leaking
tests") said, the IPv6 MTU test fails as source address selection
picking ::1. Every time we run the selftest this one report failed.
There seems not much meaning  to keep reporting a failure for 3 years
that no one plan to fix/update. Let't just skip this one first. We can
add it back when the issue fixed.
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/vrf_route_leaking.sh

@@ -565,7 +565,7 @@ EOF
 command -v ping6 > /dev/null 2>&1 && ping6=$(command -v ping6) || ping6=$(command -v ping)
 
 TESTS_IPV4="ipv4_ping_ttl ipv4_traceroute ipv4_ping_frag ipv4_ping_ttl_asym ipv4_traceroute_asym"
-TESTS_IPV6="ipv6_ping_ttl ipv6_traceroute ipv6_ping_frag ipv6_ping_ttl_asym ipv6_traceroute_asym"
+TESTS_IPV6="ipv6_ping_ttl ipv6_traceroute ipv6_ping_ttl_asym ipv6_traceroute_asym"
 
 ret=0
 nsuccess=0