checkpatch: fix networking kernel-doc block comment defect

checkpatch can generate a false positive when inserting a new kernel-doc
block and function above an existing kernel-doc block.

Fix it by checking that the context line is also a newly inserted line.

Signed-off-by: Joe Perches <joe@perches.com>
Reported-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>