selftests/bpf: Fix connect4_prog tcp/socket header type conflict

selftests/bpf: Fix connect4_prog tcp/socket header type conflict

There is a potential for us to hit a type conflict when including
netinet/tcp.h and sys/socket.h, we can replace both of these includes
with linux/tcp.h and bpf_tcp_helpers.h to avoid this conflict.

Fixes errors like the below when compiling with gcc BPF backend:

  In file included from /usr/include/netinet/tcp.h:91,
                   from progs/connect4_prog.c:11:
  /home/buildroot/opt/cross/lib/gcc/bpf/13.0.0/include/stdint.h:34:23: error: conflicting types for 'int8_t'; have 'char'
     34 | typedef __INT8_TYPE__ int8_t;
        |                       ^~~~~~
  In file included from /usr/include/x86_64-linux-gnu/sys/types.h:155,
                   from /usr/include/x86_64-linux-gnu/bits/socket.h:29,
                   from /usr/include/x86_64-linux-gnu/sys/socket.h:33,
                   from progs/connect4_prog.c:10:
  /usr/include/x86_64-linux-gnu/bits/stdint-intn.h:24:18: note: previous declaration of 'int8_t' with type 'int8_t' {aka 'signed char'}
     24 | typedef __int8_t int8_t;
        |                  ^~~~~~
  /home/buildroot/opt/cross/lib/gcc/bpf/13.0.0/include/stdint.h:43:24: error: conflicting types for 'int64_t'; have 'long int'
     43 | typedef __INT64_TYPE__ int64_t;
        |                        ^~~~~~~
  /usr/include/x86_64-linux-gnu/bits/stdint-intn.h:27:19: note: previous declaration of 'int64_t' with type 'int64_t' {aka 'long long int'}
     27 | typedef __int64_t int64_t;
        |                   ^~~~~~~

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220829154710.3870139-1-james.hilliard1@gmail.com