examples/nf-queue: handle recv error, use larger buffer

We ask for 0xffff copy size, so we need a buffer that can
hold 0xffff, plus a few more bytes to allow for netlink attributes.

Also, turn off/handle ENOBUFS.

Signed-off-by: Florian Westphal <fw@strlen.de>
src: add new GSO handling capabilities

allows userspace to ask for large gso packets via nfqueue.

Signed-off-by: Florian Westphal <fw@strlen.de>
examples/nf-queue: receive large gso packets

Signed-off-by: Florian Westphal <fw@strlen.de>
Merge branch 'next'

Get the following patches into master:

examples/nf-queue: receive large gso packets
src: add new GSO handling capabilities
examples/nf-queue: handle recv error, use larger buffer
build: avoid symbol namespace pollution

As of f40eabb01 (add pkt_buff and protocol helper functions)
libnetfilter_queue accidentally exports the internal function named
'checksum'.  This is a bit too generic and may cause crashes with
applications that worked fine before.

This patch makes the functions checksum, checksum_tcpudp_ipv4 and
checksum_tcpudp_ipv6 local by building with fvis-hidden and adding
EXPORTs for the legacy api calls and the ones that seem to have missing
EXPORT tags (mainly pktbuff api).

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
src: extra: add prefix nfq_ to internal checksum functions

These functions are internal and they belong to the libnetfilter_queue scope,
so let's add the corresponding nfq_ prefix.

Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>