[comboot] Unhook interrupt vectors after returning from a COMBOOT image

src/arch/i386/image/com32.c

 		break;
 	}
 
+	unhook_comboot_interrupts();
 	comboot_force_text_mode();
 
 	return 0;

src/arch/i386/image/comboot.c

 		break;
 	}
 
+	unhook_comboot_interrupts();
 	comboot_force_text_mode();
 
 	return 0;

src/arch/i386/include/comboot.h

 } comboot_shuffle_descriptor;
 
 extern void hook_comboot_interrupts ( );
+extern void unhook_comboot_interrupts ( );
 
 /* These are not the correct prototypes, but it doens't matter, 
  * as we only ever get the address of these functions;

src/arch/i386/interface/syslinux/comboot_call.c

 	hook_bios_interrupt ( 0x22, ( unsigned int ) int22_wrapper,
 	                      &int22_vector );
 }
+
+/**
+ * Unhook BIOS interrupts related to COMBOOT API (INT 20h, 21h, 22h)
+ */
+void unhook_comboot_interrupts ( ) {
+
+	unhook_bios_interrupt ( 0x20, ( unsigned int ) int20_wrapper,
+				&int20_vector );
+
+	unhook_bios_interrupt ( 0x21, ( unsigned int ) int21_wrapper,
+				&int21_vector );
+
+	unhook_bios_interrupt ( 0x22, ( unsigned int ) int22_wrapper,
+				&int22_vector );
+}