Do not request IPV6 routing info

Do not request IPV6 routing info

PROX is not yet dealing with IPV6 routing info (only IPV4). Hence we got
a segmentation fault when receiving such information. In a previous
commit, we are checking for IPV4 routing info and we do not continue
processing of any other routing information. With this fix, we ask the
Linux OS NOT to provide IPV6 routing info.
The checks when receiving routing information have changed so that we only
treat IPV4 and nothing else.

Change-Id: I428a036c31014377c8de08da17e51740be0e1de5
Signed-off-by: Luc Provoost <luc.provoost@intel.com>