conf: make virDomainControllerFindUnusedIndex() more generally usable

Make virDomainControllerFindUnusedIndex() a global function so that it
can be used outside domain_conf.c (as well as higher up in
domain_conf.c itself)/ Also make its DomainDef arg a const* so that
functions which only have a const* to the domain can use it.

src/conf/domain_conf.c

@@ -13717,8 +13717,8 @@ virDomainControllerFind(const virDomainDef *def,
 }
 
 
-static int
+int
-virDomainControllerFindUnusedIndex(virDomainDefPtr def, int type)
+virDomainControllerFindUnusedIndex(virDomainDef const *def, int type)
 {
     int idx = 0;
 

src/conf/domain_conf.h

@@ -2755,6 +2755,7 @@ int virDomainControllerFind(const virDomainDef *def, int type, int idx);
 int virDomainControllerFindByType(virDomainDefPtr def, int type);
 int virDomainControllerFindByPCIAddress(virDomainDefPtr def,
                                         virPCIDeviceAddressPtr addr);
+int virDomainControllerFindUnusedIndex(virDomainDef const *def, int type);
 virDomainControllerDefPtr virDomainControllerRemove(virDomainDefPtr def, size_t i);
 const char *virDomainControllerAliasFind(const virDomainDef *def,
                                          int type, int idx)

src/libvirt_private.syms

@@ -189,6 +189,7 @@ virDomainControllerDefFree;
 virDomainControllerDefNew;
 virDomainControllerFind;
 virDomainControllerFindByType;
+virDomainControllerFindUnusedIndex;
 virDomainControllerInsert;
 virDomainControllerInsertPreAlloced;
 virDomainControllerModelPCITypeToString;