core/bpf-firewall: replace bpf_firewall_supported() with bpf_program_supported()

core/bpf-firewall: replace bpf_firewall_supported() with bpf_program_supported()

Note, BPF_PROG_TYPE_CGROUP_SKB is supported since kernel v4.10, and
BPF_F_ALLOW_MULTI and program name is supported since kernel v4.15.
As our baseline on the kernel is v5.4, we can assume that the type,
flag, and naming is supported when bpf_program_supported() succeeds.