checkpatch: fix false positive on empty block comment lines

To avoid false positives in presence of SPDX-License-Identifier in
networking files it is required to increase the leeway for empty block
comment lines by one line.

For example, checking drivers/net/loopback.c which starts with

    // SPDX-License-Identifier: GPL-2.0-or-later
    /*
     * INET          An implementation of the TCP/IP protocol suite for the LINUX

rsults in an unnecessary warning

    WARNING: networking block comments don't use an empty /* line, use /* Comment...
    +/*
    + * INET                An implementation of the TCP/IP protocol suite for the LINUX

Signed-off-by: Łukasz Stelmach <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Joe Perches <[email protected]>
Cc: Bartłomiej Żolnierkiewicz  <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

scripts/checkpatch.pl

@@ -3464,7 +3464,7 @@ sub process {
 		if ($realfile =~ m@^(drivers/net/|net/)@ &&
 		    $prevrawline =~ /^\+[ \t]*\/\*[ \t]*$/ &&
 		    $rawline =~ /^\+[ \t]*\*/ &&
-		    $realline > 2) {
+		    $realline > 3) { # Do not warn about the initial copyright comment block after SPDX-License-Identifier
 			WARN("NETWORKING_BLOCK_COMMENT_STYLE",
 			     "networking block comments don't use an empty /* line, use /* Comment...\n" . $hereprev);
 		}