bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE

bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE

pahole currently only generates the btf_id for external function and
ftrace-able function.  Some functions in the bpf_tcp_ca_kfunc_ids
are static (e.g. cubictcp_init).  Thus, unless CONFIG_DYNAMIC_FTRACE
is set, btf_ids for those functions will not be generated and the
compilation fails during resolve_btfids.

This patch limits those functions to CONFIG_DYNAMIC_FTRACE.  I will
address the pahole generation in a followup and then remove the
CONFIG_DYNAMIC_FTRACE limitation.

Fixes: e78aea8b2170 ("bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc")
Reported-by: Cong Wang <[email protected]>
Reported-by: Lorenz Bauer <[email protected]>
Signed-off-by: Martin KaFai Lau <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]