net: Fix the statistics compilation

Make sure that the statisitics compilation can be done even
if some sub-statistics module is not compiled, like IPv6 or
IPv4 statistics.

Change-Id: I1a91acd70569f074d9bb3269f74ee9c6a0ea9cf7
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
5 files changed