check-package: check *.patch files

check-package: check *.patch files

Warn when the name of the patch file does not start with number (apply
order), see [1].
Warn when the patch was generated using git format-patch without -N, see
[2].
Warn when the patch file has no SoB, see [3].

[1] http://nightly.buildroot.org/#_providing_patches
[2] http://patchwork.ozlabs.org/patch/704753/
[3] http://nightly.buildroot.org/#_format_and_licensing_of_the_package_patches

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>