examples/bpf: fix build

Example BPF programs t2.c, t3.c in folder examples/bpf are
failing to compile with latest dpdk.org master.
The reason is changes in some core DPDK header files, that causes
now inclusion of x86 specific headers.
To overcome the issue, minimize inclusion of DPDK header files
into BPF source code.

Bugzilla ID: 321

Fixes: 9dfc06c26a8b ("test/bpf: add samples")
Cc: stable@dpdk.org
Reported-by: Michel Machado <michel@digirati.com.br>
Suggested-by: Michel Machado <michel@digirati.com.br>
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>