checkpatch: move duplicate sign off to separate warning type
Some maintainers prefer to allow duplicate signatures if that provides additional details about the patch flow. E.g. if the original patch author pulls the patch from the patchwork into the kernel branch, this can result in duplicate SOB tags from him, however this reflects the patch flow (one SOB for being the author, one SOB for pulling the patch, adding (and maybe fixing) tags and pushing the patch further.
To facilitate easily handling this kind of warnings, separate duplicate SOBs into the separate warning class ('DUPLICATE_SIGN_OFF').
Cc: Rob Clark robdclark@gmail.com Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org