x86/kgbd: Use NMI_VECTOR not APIC_DM_NMI

x86/kgbd: Use NMI_VECTOR not APIC_DM_NMI

BugLink: https://bugs.launchpad.net/bugs/1863019
[ Upstream commit 2591bc4e8d70b4e1330d327fb7e3921f4e070a51 ]

apic->send_IPI_allbutself() takes a vector number as argument.

APIC_DM_NMI is clearly not a vector number. It's defined to 0x400 which is
outside the vector space.

Use NMI_VECTOR instead as that's what it is intended to be.

Fixes: 82da3ff89dc2 ("x86: kgdb support")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105218.855189979@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>