util: Turn virFirewallAddRule() into a macro

Clang 3.9 refuses to compile the existing code with the
following error:

  util/virfirewall.c:425:20: error: passing an object that undergoes
                             default argument promotion to 'va_start'
                             has undefined behavior [-Werror,-Wvarargs]
      va_start(args, layer);
                     ^
  util/virfirewall.c:420:37: note: parameter of type 'virFirewallLayer'
                             is declared here
                     virFirewallLayer layer,
                                      ^

This happens because 'layer' is of type virFirewallLayer, which
is an enum type and not a standard type such as eg. void* or int.

To solve the issue, turn virFirewallAddRule() from a very thin
wrapper around virFirewallAddRuleFullV() to a macro that expands
to a call to virFirewallAddRuleFull() - itself a very thin wrapper
around the aforementioned virFirewallAddRuleFullV() - with no loss
of functionality or type safety.

src/libvirt_private.syms

@@ -1624,7 +1624,6 @@ virFindFileInPath;
 
 
 # util/virfirewall.h
-virFirewallAddRule;
 virFirewallAddRuleFull;
 virFirewallApply;
 virFirewallFree;

src/util/virfirewall.c

@@ -405,29 +405,6 @@ virFirewallAddRuleFullV(virFirewallPtr firewall,
     return NULL;
 }
 
-/**
- * virFirewallAddRule:
- * @firewall: firewall ruleset to add to
- * @layer: the firewall layer to change
- * @...: NULL terminated list of strings for the rule
- *
- * Add any type of rule to the firewall ruleset.
- *
- * Returns the new rule
- */
-virFirewallRulePtr
-virFirewallAddRule(virFirewallPtr firewall,
-                   virFirewallLayer layer,
-                   ...)
-{
-    virFirewallRulePtr rule;
-    va_list args;
-    va_start(args, layer);
-    rule = virFirewallAddRuleFullV(firewall, layer, false, NULL, NULL, args);
-    va_end(args);
-    return rule;
-}
-
 
 /**
  * virFirewallAddRuleFull:

src/util/virfirewall.h

@@ -44,10 +44,18 @@ virFirewallPtr virFirewallNew(void);
 
 void virFirewallFree(virFirewallPtr firewall);
 
-virFirewallRulePtr virFirewallAddRule(virFirewallPtr firewall,
+/**
-                                      virFirewallLayer layer,
+ * virFirewallAddRule:
-                                      ...)
+ * @firewall: firewall ruleset to add to
-    ATTRIBUTE_SENTINEL;
+ * @layer: the firewall layer to change
+ * @...: NULL terminated list of strings for the rule
+ *
+ * Add any type of rule to the firewall ruleset.
+ *
+ * Returns the new rule
+ */
+#define virFirewallAddRule(firewall, layer, ...) \
+        virFirewallAddRuleFull(firewall, layer, false, NULL, NULL, __VA_ARGS__)
 
 typedef int (*virFirewallQueryCallback)(virFirewallPtr firewall,
                                         const char *const *lines,