func PrevIP(ip net.IP) net.IP {
	i := ipToInt(ip)
	return intToIP(i.Sub(i, big.NewInt(1)))
}
PrevIP returns IP decremented by 1
package ip
import (
	"math/big"
	"net"
)
func NextIP(ip net.IP) net.IP {
	i := ipToInt(ip)
	return intToIP(i.Add(i, big.NewInt(1)))
}