Merge branch 'icmp_frag'

Andy Zhou says:

====================
fragmentation ICMP

Currently, we send ICMP packets when errors occur during fragmentation or
de-fragmentation.  However, it is a bug when sending those ICMP packets
in the context of using netfilter for bridging.

Those ICMP packets are only expected in the context of routing, not in
bridging mode.

The local stack is not involved in bridging forward decisions, thus
should be not used for deciding the reverse path for those ICMP messages.

This bug only affects IPV4, not in IPv6.

v1->v2:  restructure the patches into two patches that fix defragmentation and
         fragmentation respectively.

	 A bit is add in IPCB to control whether ICMP packet should be
	 generated for defragmentation.

	 Fragmentation ICMP is now removed by restructuring the
	 ip_fragment() API.

v2->v3:  Add droping icmp for bridging contrack users
         drop exporting ip_fragment() API.

v3->v4:  Remove unnecessary parentheses in 'return' statements

v4->v5:  Drop the patch that sets and checks a bit in IPCB
         that prevents ip_defrag to send ICMP.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>