iproute: print more verbose error on route cache flush

Before:
kda@vfirst ~/devel/iproute2 $ ./ip/ip route flush cache
Cannot open "/proc/sys/net/ipv4/route/flush"

After:
kda@vfirst ~/devel/iproute2/ip $ ./ip route flush cache
Cannot open "/proc/sys/net/ipv4/route/flush": Permission denied

Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
1 file changed