bpf: change prototype of bpf_session_{cookie,is_return}

bpf: change prototype of bpf_session_{cookie,is_return}

Add the function argument of "void *ctx" to bpf_session_cookie() and
bpf_session_is_return(), which is a preparation of the next patch.

The two kfunc is seldom used now, so it will not introduce much effect
to change their function prototype.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20260124062008.8657-4-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>