Merge branch 'netlink_ext_ACK'

Johannes Berg says:

====================
netlink extended ACK reporting

Changes since v4:
 * use __NLMSGERR_ATTR_MAX instead of NUM_NLMSGERR_ATTRS

Changes since v3:
 * Add NLM_F_CAPPED and NLM_F_ACK_TLVS flags, to allow entirely
   stateless parsing of the ACK messages by looking at the new
   flags. Need to check NLM_F_ACK_TLVS first, since capping can
   be done in kernels before this patchset without setting the
   flag.
 * Remove "missing_attr" functionality - this can obviously be
   added back rather easily, but I'd rather have more discussion
   about the nesting problem there.
 * Improve documentation of NLMSGERR_ATTR_OFFS
 * Improve message structure documentation, documenting that the
   request message is always capped for success cases
 * fix nlmsg_len of the outer message by calling nlmsg_end()
 * fix memcpy() of the request in success cases, going back to
   the original code that I'd changed before due to the payload
   adjustments that I reverted when introducing tlvlen

Changes since v2:
 * add NUM_NLMSGERR_ATTRS, NLMSGERR_ATTR_MAX
 * fix cookie length to 20 (sha-1 length)
 * move struct members for cookie to patch 3 where they should be
 * another cleanup suggested by David Ahern

Changes since v1:
 * credit Pablo and Jamal
 * incorporate suggestion from David Ahern
 * fix compilation in decnet
====================

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