selftests/bpf: Enlarge select() timeout for test_maps

0Day robot observed that it's easily timeout on a heavy load host.
-------------------
# selftests: bpf: test_maps
# Fork 1024 tasks to 'test_update_delete'
# Fork 1024 tasks to 'test_update_delete'
# Fork 100 tasks to 'test_hashmap'
# Fork 100 tasks to 'test_hashmap_percpu'
# Fork 100 tasks to 'test_hashmap_sizes'
# Fork 100 tasks to 'test_hashmap_walk'
# Fork 100 tasks to 'test_arraymap'
# Fork 100 tasks to 'test_arraymap_percpu'
# Failed sockmap unexpected timeout
not ok 3 selftests: bpf: test_maps # exit=1
# selftests: bpf: test_lru_map
# nr_cpus:8
-------------------
Since this test will be scheduled by 0Day to a random host that could have
only a few cpus(2-8), enlarge the timeout to avoid a false NG report.

In practice, i tried to pin it to only one cpu by 'taskset 0x01 ./test_maps',
and knew 10S is likely enough, but i still perfer to a larger value 30.

Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Li Zhijian <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/test_maps.c

···
 
 		FD_ZERO(&w);
 		FD_SET(sfd[3], &w);
-		to.tv_sec = 1;
+		to.tv_sec = 30;
 		to.tv_usec = 0;
 		s = select(sfd[3] + 1, &w, NULL, NULL, &to);
 		if (s == -1) {