checkpatch: warn when networking block comment lines don't start with *

Some block comments in network are written as:

	/* block comment line 1
	   block comment line 2
	 */

Emit a warning on the "block comment line 2" because it should be

	/* block comment line 1
	 * block comment line 2
	 */

This warning is only emitted on the second line of a block comment.

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>