selftests/bpf: Move common TCP helpers into bpf_tracing_net.h

selftests/bpf: Move common TCP helpers into bpf_tracing_net.h

Some BPF selftests contain identical copies of the min(), max(),
before(), and after() helpers. These repeated snippets are the same
across the tests and do not need to be defined separately.

Move these helpers into bpf_tracing_net.h so they can be shared by
TCP related BPF programs. This removes repeated code and keeps the
helpers in a single place.

Reviewed-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Hoyeon Lee <hoyeon.lee@suse.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20251115225550.1086693-4-hoyeon.lee@suse.com