Add comment that bpfread() has multi-threading issues.

Fix minor white space nit.

sys/net/bpf.c

@@ -562,6 +562,10 @@ bpfread(struct cdev *dev, struct uio *uio, int ioflag)
 	 * Move data from hold buffer into user space.
 	 * We know the entire buffer is transferred since
 	 * we checked above that the read buffer is bpf_bufsize bytes.
+	 *
+	 * XXXRW: More synchronization needed here: what if a second thread
+	 * issues a read on the same fd at the same time?  Don't want this
+	 * getting invalidated.
 	 */
 	error = uiomove(d->bd_hbuf, d->bd_hlen, uio);
 
@@ -574,7 +578,6 @@ bpfread(struct cdev *dev, struct uio *uio, int ioflag)
 	return (error);
 }
 
-
 /*
  * If there are processes sleeping on this descriptor, wake them up.
  */