opts: remove unused IPOpt option

This option was created Moby [6d59a56], and
used for the daemon config [353b7c8]. It was
migrated from the Moby repository in f34ca0a,
but was never used by the CLI, and there are no external consumers.

If we would need an IP-address option, spf13/pflags now provides those, so
there's no need to implement this ourselves.

[6d59a56]: moby/moby@6d59a56
[353b7c8]: moby/moby@353b7c8

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah