checkpatch: ignore email headers better

checkpatch: ignore email headers better

There are some patches created by git format-patch that when scanned by
checkpatch report errors on lines like

To:	address.tld

This is a checkpatch false positive.

Improve the logic a bit to ignore folded email headers to avoid emitting
these messages.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20180430124651.10340-4-stefanha@redhat.com
(cherry picked from commit 29ee1b0c67e0dd7dea8dd718e8326076bce5b6fe)
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>