ospfd: Some small tweaks to the SPF execution reason patch

* ospf_spf.h: use an enum for the reason, and have it as a new argument to
  ospf_spf_calculate_schedule, no need for additional call, and let compiler
  do the checking.
* ospf_spf.c: format changes - Quagga coding style places function names
  at the start of a new line, for easy grepping for definition.
  (ospf_spf_calculate_timer) Change the log format of SPF execution time to
  avoid ginormous line, and make logging conditional, as is the norm.
diff --git a/ospfd/ospf_ase.c b/ospfd/ospf_ase.c
index 9038b3a..8aedc80 100644
--- a/ospfd/ospf_ase.c
+++ b/ospfd/ospf_ase.c
@@ -679,7 +679,7 @@
 
       quagga_gettime(QUAGGA_CLK_MONOTONIC, &stop_time);
 
-      zlog_info ("SPF Processing Time(usecs): External Routes: %d\n",
+      zlog_info ("SPF Processing Time(usecs): External Routes: %ld\n",
 		 (stop_time.tv_sec - start_time.tv_sec)*1000000L+
 		 (stop_time.tv_usec - start_time.tv_usec));
     }