ip route change dev tap0 192.168.7.0/24 rto_min 1ms
Error: argument "1ms" is wrong: "rto_min" value is invalid

get_time_rtt() checks for 's' or 'msec' and converts to milliseconds
if needed.

Fixes: 697ac639 (utils: fix range checking for get_u32/get_u64 et all)
Signed-off-by: Florian Westphal <fw@strlen.de>