UBUNTU: SAUCE: (no-up) nbd: Change default partitions per device to 15

UBUNTU: SAUCE: (no-up) nbd: Change default partitions per device to 15

This was previously changed by using an "options" line in a modprobe.d
file, however that practice is now deprecated.  This is because module
names, option names, their values and even their current defaults can
all change inside the kernel and module-init-tools has never been kept
in sync.

In addition, changing the kernel means that the option change will apply
if the module is built in by users or the OEM team.

Bug: #342563

Signed-off-by: Scott James Remnant <scott@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>