selftests/bpf: Use connect_to_addr in test_sock_addr

This patch uses public network helper connect_to_addr() exported in
network_helpers.h instead of the local defined function connect_to_server()
in test_sock_addr.c. This can avoid duplicate code.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/f263797712d93fdfaf2943585c5dfae56714a00b.1713868264.git.tanggeliang@kylinos.cn


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>