zdtm/net/ipv4: replace rand limits with rand ranges

some sysctls have minimal value != 0 so we will also need to
set their lower limit e.g. /proc/sys/net/ipv6/conf/all/mtu

name                    possible states         range

accept_source_route     "<0", ">=0"             {-1, 0}
medium_id               "-1", "0", ">0"         {-1, INT_MAX}
src_valid_mark          true, false             {0, 1}
tag                     any                     {INT_MIN, INT_MAX}

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Reviewed-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>