add priority bit to descriptor flags fields for high priority (e.g. control) messages

the bmi should attempt to deliver these at a higher priority than other traffic 

This commit was SVN r6063.

src/mca/bmi/bmi.h

@@ -180,6 +180,7 @@ OBJ_CLASS_DECLARATION(mca_bmi_base_descriptor_t);
                                                                                                                
 #define MCA_BMI_DES_FLAGS_BMI  0x0001
 #define MCA_BMI_DES_FLAGS_PML  0x0002
+#define MCA_BMI_DES_FLAGS_PRIORITY 0x0004
 #define MCA_BMI_DES_MAX_SEGMENTS 16