FIX: irqbalance settings

By default irqbalance should be honoring isolcpu settings but as of
latest finding IRQs are distributed ad-hoc even if irqbalance is:
- enabled: with default settings
- disabled: by configuration
- disabled: as a service
- enabled: with incorrect mask

This patch brings explicit configuration of IRQBALANCE_BANNED_CPUS with
mask large enough to cover all cores and keeps IRQ to be processed by
core 0.

Signed-off-by: Peter Mikus <pmikus@cisco.com>
Change-Id: I0eb36d780feb284a5493e123acbf993a362ea9ec