selftests: net: Correct ping6 expected rc from 2 to 1

selftests: net: Correct ping6 expected rc from 2 to 1

./fcnal-test.sh -v -t ipv6_ping
TEST: ping out, VRF bind - ns-B IPv6 LLA                                      [FAIL]
TEST: ping out, VRF bind - multicast IP                                       [FAIL]

ping6 is failing as it should.
COMMAND: ip netns exec ns-A /bin/ping6 -c1 -w1 fe80::7c4c:bcff:fe66:a63a%red
strace of ping6 shows it is failing with '1',
so change the expected rc from 2 to 1.

Fixes: 1fdd5f0dd4ed ("selftests: Add ipv6 ping tests to fcnal-test")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Jie2x Zhou <jie2x.zhou@intel.com>
Link: https://lore.kernel.org/r/20211209020230.37270-1-jie2x.zhou@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>