Import an upstream fix for a DDoS vulnerability in the
network plugin: CVE-2017-7401

Refresh patches.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

Buildbot revealed that Collectd 5.7.1 uses libcap to evaluate system
capabilities and display advice on some plugins (dns, iptables, exec,
ping, ceph, turbostat).

Disable the check in configure.ac in order to avoid a dependency
for libcap. (It is not that big, only 6 kB .ipk, but still avoid that.)

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>