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_asbr.c b/ospfd/ospf_asbr.c
index dbf7f11..8bef175 100644
--- a/ospfd/ospf_asbr.c
+++ b/ospfd/ospf_asbr.c
@@ -264,8 +264,7 @@
     }
 
   /* Transition from/to status ASBR, schedule timer. */
-  ospf_flag_spf_reason (SPF_FLAG_ASBR_STATUS_CHANGE);
-  ospf_spf_calculate_schedule (ospf);
+  ospf_spf_calculate_schedule (ospf, SPF_FLAG_ASBR_STATUS_CHANGE);
   ospf_router_lsa_update (ospf);
 }