selftests/bpf: Fix sk lookup usage in test_sock_addr

Semantic of netns_id argument of bpf_sk_lookup_tcp and bpf_sk_lookup_udp
was changed (fixed) in f71c6143. Corresponding changes have to be
applied to all call sites in selftests. The patch fixes corresponding
call sites in test_sock_addr test: pass BPF_F_CURRENT_NETNS instead of 0
in netns_id argument.

Fixes: f71c6143 ("bpf: Support sk lookup in netns with id 0")
Reported-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Joe Stringer <joe@wand.net.nz>
Tested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>