selftests/bpf: Improve tc_tunnel test reliability

A test failure was discovered in BPF CI [1] caused by connection timeout.
The current test timeout of 500ms is insufficient for CI environments,
particularly under high load.

While the optimal timeout is unclear, this test was converted from the
original test_tc_tunnel.sh script. The original script used nc with "-w 1"
to specify a 1-second timeout [2]. Therefore, this test restores the
timeout to 1s.

Test:
./test_progs -a tc_tunnel
#478/1 tc_tunnel/ipip_none:OK
#478/2 tc_tunnel/ipip6_none:OK
#478/3 tc_tunnel/ip6tnl_none:OK
#478/4 tc_tunnel/sit_none:OK
#478/5 tc_tunnel/vxlan_eth:OK
#478/6 tc_tunnel/ip6vxlan_eth:OK
#478/7 tc_tunnel/gre_none:OK
#478/8 tc_tunnel/gre_eth:OK
#478/9 tc_tunnel/gre_mpls:OK
#478/10 tc_tunnel/ip6gre_none:OK
#478/11 tc_tunnel/ip6gre_eth:OK
#478/12 tc_tunnel/ip6gre_mpls:OK
#478/13 tc_tunnel/udp_none:OK
#478/14 tc_tunnel/udp_eth:OK
#478/15 tc_tunnel/udp_mpls:OK
#478/16 tc_tunnel/ip6udp_none:OK
#478/17 tc_tunnel/ip6udp_eth:OK
#478/18 tc_tunnel/ip6udp_mpls:OK
#478 tc_tunnel:OK
Summary: 1/18 PASSED, 0 SKIPPED, 0 FAILED

[1] https://github.com/kernel-patches/bpf/actions/runs/22674350732/job/65728072723
[2] https://lore.kernel.org/all/20251027-tc_tunnel-v3-4-505c12019f9d@bootlin.com/

Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Link: https://lore.kernel.org/r/20260312083615.31835-1-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>