Merge branch 'debug-net'

Eric Dumazet says:

====================
net: CONFIG_DEBUG_NET and friends

This patch series is inspired by some syzbot reports
hinting that skb transport_header might be not set
in places we expect it being set.

Add a new CONFIG_DEBUG_NET option
and DEBUG_NET_WARN_ON_ONCE() helper, so that we can start
adding more sanity checks in the future.

Replace two BUG() in skb_checksum_help()
with less risky code.

v2: make first patch compile on more arches/compilers
    add the 5th patch to add more debugging in skb_checksum_help()
====================

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