more bpf samples build breakage...

Inlcuding bpf_util.h into test_pkt_access.c et al. broke the build even
more so than it already is on sparc.

The problem is we end up including all the stdio.h bits and eventually
hit things like:

In file included from /usr/include/stdio.h:933:
/usr/include/bits/stdio-ldbl.h:28:20: error: cannot apply asm label to function after its first use
__LDBL_REDIR_DECL (vfprintf)
~~~~~~~~~~~~~~~~~~~^~~~~~~~~
/usr/include/sys/cdefs.h:373:26: note: expanded from macro '__LDBL_REDIR_DECL'
  extern __typeof (name) name __asm (__ASMNAME ("__nldbl_" #name));

So please let's put CLANG compiled helpers into header files
specifically meant to be included by CLANG compiled BPF programs
rather than the host build environment.