kni: fix build on Ubuntu 12.04
kni: fix build on Ubuntu 12.04

On Ubuntu 12.04.4 file '/proc/version_signature' contains
'Ubuntu 3.11.0-15.25~precise1-generic 3.11.10'. This introduce compilation
error since '~precise1' will not be discarded. This patch discards
everything after '~' inclusively.

Signed-off-by: Pawel Wodkowski <ee43875f918ccc633a652e6e256df4e6d9c42850@intel.com>
Acked-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

mixja/dpdk,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,msune/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,venkynv/dpdk-mirror,msune/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,mixja/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,mixja/dpdk,msune/dpdk