checkpatch: ignore automatically imported Linux headers

Linux uses tabs for indentation and checkpatch always complained about
automatically imported headers.  update-linux-headers.sh could be modified to
expand tabs, but there is no real reason to complain about any ugly code in
Linux headers, so skip all hunk-related checks.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
