selftests: forwarding: Switch off timeout

selftests: forwarding: Switch off timeout

The default timeout for selftests is 45 seconds, but it is not enough
for forwarding selftests which can takes minutes to finish depending on
the number of tests cases:

 # make -C tools/testing/selftests TARGETS=net/forwarding run_tests
 TAP version 13
 1..102
 # timeout set to 45
 # selftests: net/forwarding: bridge_igmp.sh
 # TEST: IGMPv2 report 239.10.10.10                                    [ OK ]
 # TEST: IGMPv2 leave 239.10.10.10                                     [ OK ]
 # TEST: IGMPv3 report 239.10.10.10 is_include                         [ OK ]
 # TEST: IGMPv3 report 239.10.10.10 include -> allow                   [ OK ]
 #
 not ok 1 selftests: net/forwarding: bridge_igmp.sh # TIMEOUT 45 seconds

Fix by switching off the timeout and setting it to 0. A similar change
was done for BPF selftests in commit 6fc5916cc256 ("selftests: bpf:
Switch off timeout").

Fixes: 81573b18f26d ("selftests/net/forwarding: add Makefile to install tests")
Reported-by: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
Closes: https://lore.kernel.org/netdev/8d149f8c-818e-d141-a0ce-a6bae606bc22@alu.unizg.hr/
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Tested-by: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20230808141503.4060661-3-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>