netfilter: nf_nat_core: eliminate useless find_appropriate_src for IP_NAT_RANGE_PROTO_RANDOM

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>