Int64 will cause OutOfRange

[arctan90]

hybridnet/pkg/utils/cidr.go

Line 76 in 34d622b

return big.NewInt(0).Abs(big.NewInt(0).Sub(bi, ai)).Int64() + 1

Ipv6 address is 128bits, but 64bits of Int64, considering this circumstances

a := net.ParseIP("2001:db8:acad:3::101")
b := net.ParseIP("2001:db8:acad:3:ffff:ffff:ffff:fffe")
out := Capacity(a, b) // out is -258

then in subnet webhook, validating will pass. An over ranged subnet will be created, and causing OOM when loading IPs of subnet into ipslce by the following code

//  /pkg/ipam/types/subnet.go Line 286

	// generate valid Available IP Slice
	s.AvailableIPs = NewIPSlice()
	for i := s.Start; utils.Cmp(i, s.End) <= 0; i = utils.NextIP(i) {
		if !s.Contains(i) {
			continue
		}
		// ignore reserved ip
		if s.IsReservedIP(i.String()) {
			continue
		}
		s.AvailableIPs.Add(i.String(), i.Equal(s.LastAllocatedIP))
	}