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 <l.stelmach@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Joe Perches <joe@perches.com>
Cc: Bartłomiej Żolnierkiewicz  <b.zolnierkie@samsung.co>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lkml.kernel.org/r/20201006083509.19934-1-l.stelmach@samsung.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>