znc: add patch to add missing <time.h> inclusions

With certain toolchains, znc fails to build due to missing <time.h>
inclusions. This commit fixes that by adding a patch that adds those
missing inclusions.

Fixes:

  http://autobuild.buildroot.net/results/86e/86e5e76a6ccc1396cd84107af63cdaa0ce1dfbee/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>