x86, apic, 32-bit: add self-IPI methods

Impact: fix rare crash on 32-bit

The 32-bit APIC drivers had their send_IPI_self vectors set to NULL,
but ioapic_retrigger_irq() depends on it being always set. Fix it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/probe_32.c b/arch/x86/kernel/probe_32.c
index 3f12a40..22337b7 100644
--- a/arch/x86/kernel/probe_32.c
+++ b/arch/x86/kernel/probe_32.c
@@ -116,7 +116,7 @@
 	.send_IPI_mask_allbutself	= default_send_IPI_mask_allbutself_logical,
 	.send_IPI_allbutself		= default_send_IPI_allbutself,
 	.send_IPI_all			= default_send_IPI_all,
-	.send_IPI_self			= NULL,
+	.send_IPI_self			= default_send_IPI_self,
 
 	.wakeup_cpu			= NULL,
 	.trampoline_phys_low		= DEFAULT_TRAMPOLINE_PHYS_LOW,