Ubuntu installer doesn't allow setting swap higher than 2GB

[Stanley Phoong]

Installed Ubuntu 18.04 final release and I tried setting up a swap with the pre-seed config but the swap value fails to go above 2GB.

Here's my configuration:

```
## Partitioning regular
d-i partman-auto/disk string /dev/sda
d-i partman-auto/method string regular
d-i partman-auto/choose_recipe select atomic

# Swap Memory
d-i partman-auto/cap-ram string 4096
d-i partman-basicfilesystems/no_swap boolean false
#d-i partman-swapfile/percentage string 50
d-i partman-swapfile/size string 4096

# This makes partman automatically partition without confirmation, provided
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
```

I've seen others facing similar issues and their recommendation was to use `d-i partman-auto/cap-ram` to configure the value but I've tried setting it to false as well as a larger value and it still doesn't work.

What we are expected to see if the swap value increase to 4GB as shown in the pre-seed config.

Possible related issue: https://bugs.launchpad.net/ubuntu/+source/partman-auto/+bug/1767299

Any help?