x86: avoid wrong use of all-but-self IPI shorthand

x86: avoid wrong use of all-but-self IPI shorthand

With "nosmp" I did observe a flood of "APIC error on CPU0: 04(04), Send
accept error" log messages on an AMD system. And rightly so - nothing
excludes the use of the shorthand in send_IPI_mask() in this case. Set
"unaccounted_cpus" to "true" also when command line restrictions are the
cause.

Note that PV-shim mode is unaffected by this change, first and foremost
because "nosmp" and "maxcpus=" are ignored in this case.

Fixes: 5500d265a2a8 ("x86/smp: use APIC ALLBUT destination shorthand when possible")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>