bpf: move bpf_prog to bpf.h

bpf: move bpf_prog to bpf.h

In order to add a version of bpf_prog_run_array which accesses the
bpf_prog->aux member, bpf_prog needs to be more than a forward
declaration inside bpf.h.

Given that filter.h already includes bpf.h, this merely reorders
the type declarations for filter.h users. bpf.h users now have access to
bpf_prog internals.

Signed-off-by: Delyan Kratunov <delyank@fb.com>
Link: https://lore.kernel.org/r/3ed7824e3948f22d84583649ccac0ff0d38b6b58.1655248076.git.delyank@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>