In e6f30c7 ("netfilter: x_tables: add xt_bpf match"), the internal
linux/filter.h header slipped through in the user exposed xt_bpf.h
header as included file.

is that true? #include <linux/filter.h> should include
include/uapi/linux/filter.h in userspace builds.

+struct sk_filter;
+
 struct xt_bpf_info {
        __u16 bpf_program_num_elem;
        struct sock_filter bpf_program[XT_BPF_MAX_NUM_INSTR];

I think include/uapi/linux/filter.h is still needed for the definition
of struct sock_filter.

The uapi file does not declare sk_filter, so we do need to add the
forward declaration. Thanks, Pablo.