selftests/bpf: Sanitize the SEC and inline usages in the bpf-tcp-cc tests

It is needed to remove the BPF_STRUCT_OPS usages from the tcp-cc tests
because it is defined in bpf_tcp_helpers.h which is going to be retired.
While at it, this patch consolidates all tcp-cc struct_ops programs to
use the SEC("struct_ops") + BPF_PROG().

It also removes the unnecessary __always_inline usages from the
tcp-cc tests.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20240509175026.3423614-5-martin.lau@linux.dev


Signed-off-by: Alexei Starovoitov <ast@kernel.org>