bpfilter: remove extra header search paths for bpfilter_umh

Currently, the header search paths -Itools/include and
-Itools/include/uapi are not used. Let's drop the unused code.

We can remove -I. too by fixing up one C file.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>