MAINTAINERS: Update XDP and AF_XDP entries

Getting too many false positive matches with current use
of the content regex K: and file regex N: patterns.

This patch drops file match N: and makes K: more restricted.
Some more normal F: file wildcards are added.

Notice that AF_XDP forgot to some F: files that is also
updated in this patch.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/bpf/160586238944.2808432.4401269290440394008.stgit@firesoul