We are going to add kern_flags field in redirect_info for kernel
internal use.
In order to avoid function call to access the flags, make redirect_info
accessible from modules. Also as it is now non-static, add prefix bpf_
to redirect_info.

v6:
- Fix sparse warning around EXPORT_SYMBOL.
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>