selftests/net: convert vrf_route_leaking.sh to run it in unique namespace

Here is the test result after conversion.

]# ./vrf_route_leaking.sh

###########################################################################
IPv4 (sym route): VRF ICMP ttl error route lookup ping
###########################################################################

TEST: Basic IPv4 connectivity [ OK ]
TEST: Ping received ICMP ttl exceeded [ OK ]

...

TEST: Basic IPv6 connectivity [ OK ]
TEST: Traceroute6 reports a hop on r1 [ OK ]

Tests passed: 18
Tests failed: 0

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: vrf_route_leaking: remove ipv6_ping_frag from default testing

As the initial commit 1a01727676a8 ("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>

selftests: Add VRF route leaking tests

The objective of the tests is to check that ICMP errors generated while
crossing between VRFs are properly routed back to the source host.

The first ttl test sends a ping with a ttl of 1 from h1 to h2 and parses the
output of the command to check that a ttl expired error is received.

The second ttl test runs traceroute from h1 to h2 and parses the output to
check for a hop on r1.

The mtu test sends a ping with a payload of 1450 from h1 to h2, through
r1 which has an interface with a mtu of 1400 and parses the output of the
command to check that a fragmentation needed error is received.

[ The IPv6 MTU test still fails with the symmetric routing setup. It
appears to be caused by source address selection picking ::1. Fixing
this is beyond the scope of this series. ]

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>