selftests/net: convert fcnal-test.sh to run it in unique namespace

selftests/net: convert fcnal-test.sh to run it in unique namespace

Here is the test result after conversion. There are some failures, but it
also exists on my system without this patch. So it's not affectec by
this patch and I will check the reason later.

  ]# time ./fcnal-test.sh
  /usr/bin/which: no nettest in (/root/.local/bin:/root/bin:/usr/share/Modules/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin)

  ###########################################################################
  IPv4 ping
  ###########################################################################

  #################################################################
  No VRF

  SYSCTL: net.ipv4.raw_l3mdev_accept=0

  TEST: ping out - ns-B IP                                                      [ OK ]
  TEST: ping out, device bind - ns-B IP                                         [ OK ]
  TEST: ping out, address bind - ns-B IP                                        [ OK ]
  ...

  #################################################################
  SNAT on VRF

  TEST: IPv4 TCP connection over VRF with SNAT                                  [ OK ]
  TEST: IPv6 TCP connection over VRF with SNAT                                  [ OK ]

  Tests passed: 893
  Tests failed:  21

  real    52m48.178s
  user    0m34.158s
  sys     1m42.976s

BTW, this test needs a really long time. So expand the timeout to 1h.

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://lore.kernel.org/r/20231213060856.4030084-6-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>