x86/IRQ: avoid UB (or worse) in trace_irq_mask()

x86/IRQ: avoid UB (or worse) in trace_irq_mask()

Dynamically allocated CPU mask objects may be smaller than cpumask_t, so
copying has to be restricted to the actual allocation size. This is
particulary important since the function doesn't bail early when tracing
is not active, so even production builds would be affected by potential
misbehavior here.

Take the opportunity and also
- use initializers instead of assignment + memset(),
- constify the cpumask_t input pointer,
- u32 -> uint32_t.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>