pkt_sched: Fix return value corruption in HTB and TBF.

pkt_sched: Fix return value corruption in HTB and TBF.

[ Upstream commit 69747650c814a8a79fef412c7416adf823293a3e ]

Based upon a bug report by Josip Rodin.

Packet schedulers should only return NET_XMIT_DROP iff
the packet really was dropped.  If the packet does reach
the device after we return NET_XMIT_DROP then TCP can
crash because it depends upon the enqueue path return
values being accurate.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>