scripts: report on author emails that are mangled by the mailing list

In some cases the Author: email address in patches submitted to the
list gets mangled such that it says

    John Doe via Qemu-devel <qemu-devel@nongnu.org>

This change is a result of workarounds for DMARC policies.

Subsystem maintainers accepting patches need to catch these and fix
them before sending pull requests, so a checkpatch.pl test is highly
desirable.
Reviewed-by: NEric Blake <eblake@redhat.com>
Acked-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

scripts/checkpatch.pl

@@ -1402,6 +1402,10 @@ sub process {
 			$is_patch = 1;
 		}
 
+		if ($line =~ /^Author: .*via Qemu-devel.*<qemu-devel\@nongnu.org>/) {
+		    ERROR("Author email address is mangled by the mailing list\n" . $herecurr);
+		}
+
 #check the patch for a signoff:
 		if ($line =~ /^\s*signed-off-by:/i) {
 			# This is a signoff, if ugly, so do not double report.