ospfd: compile warning cleanups

A set of patches to clarify some comments as well as cleanup code that was
causing warnings.  After these patches, the code can be compiled with

-Wall -Wsign-compare -Wpointer-arith -Wbad-function-cast -Wwrite-strings
-Wmissing-prototypes -Wmissing-declarations -Wchar-subscripts -Wcast-qual
-Wextra -Wno-unused-parameter -Wno-missing-field-initializers

(what is current in trunk plus -Wextra -Wno-unused-parameter
-Wno-missing-field-initializers).

Signed-off-by: Scott Feldman <sfeldma@cumulusnetworks.com>
diff --git a/ospfd/ospf_apiserver.c b/ospfd/ospf_apiserver.c
index 84d70cc..db1ccda 100644
--- a/ospfd/ospf_apiserver.c
+++ b/ospfd/ospf_apiserver.c
@@ -299,13 +299,10 @@
 ospf_apiserver_event (enum event event, int fd,
 		      struct ospf_apiserver *apiserv)
 {
-  struct thread *apiserver_serv_thread;
-
   switch (event)
     {
     case OSPF_APISERVER_ACCEPT:
-      apiserver_serv_thread =
-	thread_add_read (master, ospf_apiserver_accept, apiserv, fd);
+      (void)thread_add_read (master, ospf_apiserver_accept, apiserv, fd);
       break;
     case OSPF_APISERVER_SYNC_READ:
       apiserv->t_sync_read =