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_opaque.c b/ospfd/ospf_opaque.c
index aa126e1..744952c 100644
--- a/ospfd/ospf_opaque.c
+++ b/ospfd/ospf_opaque.c
@@ -223,9 +223,15 @@
     default:
       if (OPAQUE_TYPE_RANGE_UNASSIGNED (opaque_type))
         name = "Unassigned";
-      /* XXX warning: comparison is always true due to limited range of data type */
-      else if (OPAQUE_TYPE_RANGE_RESERVED (opaque_type))
-        name = "Private/Experimental";
+      else
+        {
+          u_int32_t bigger_range = opaque_type;
+          /*
+           * Get around type-limits warning: comparison is always true due to limited range of data type
+           */
+          if (OPAQUE_TYPE_RANGE_RESERVED (bigger_range))
+            name = "Private/Experimental";
+        }
       break;
     }
   return name;