conntrack: compare: relax MARK/ZONE attribute comparision

Relax checking for MARK and ZONE to treat 'attribute not
set' like 'attribute is set to 0'.

This matches kernel behaviour, conntracks are always in zone 0,
except if specified differently.  Same for connmark.

The kernel will also not include the zone/mark attributes in dumps
unless they have non-zero values.

This makes qa/test_api pass again with the updated test cases.

Reported-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>
Signed-off-by: Florian Westphal <fw@strlen.de>
conntrack: api: add two new bitmask functions

This patch adds two functions, useful for ulogd IPFIX
output module.

Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>
Signed-off-by: Florian Westphal <fw@strlen.de>
qa: add tests for new bitmask functions

for nfct_bitmask_clear() and nfct_bitmask_equal()

Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>
Signed-off-by: Florian Westphal <fw@strlen.de>
qa: build unshared nfct environment

nssocket forks new netns child and set network environment defined in
nssocket.h

    * connect parent by veth peer
    * device names and addresses are VETH_...
    * set default gateway device to dummy, named DUMMY_LINK_NAME

It enables get socket fd from child ns by nssocket(), see example
ct_tcp_event.c

Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>
qa: use nfct_get_attr_u instead of raw nfct_get_attr()
qa: introduce testcb_common()
qa: introduce author_ct()

always can not find good name...
qa: introduce testcb_ipv4_addr()
qa: introduce testcb_port()
qa: move timeout setting out from common
qa: rename utility functions
qa: export and move assert utility functions.
qa: change testcb name to be understandable
qa: update understandable (for me)
qa: use c99 array instead of alloca
qa: assume netns has been prepared by ip(8) before test
qa: minor cleanups