samples/bpf: use hugepages in xdpsock app

This patch modifies xdpsock to use mmap instead of posix_memalign. With
this change, we can use hugepages when running the application in unaligned
chunks mode. Using hugepages makes it more likely that we have physically
contiguous memory, which supports the unaligned chunk mode better.

Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>