glib-aux: define nm_direct_hash/nm_str_hash as macros

nm_hash_str() has the proper name and signature for that it does.
That is, it has a "nm_hash_*" prefix and the parameter is of type
"const char *".
nm_hash_str() has this name because it is primarily about hashing.

For hash tables, glib has g_str_hash() and g_str_equal(). We want
to replace g_str_hash() with our implementation (nm_hash_str()) because
that uses siphash24 with a random seed.
But in those cases we want to use the more familiar name "nm_str_hash()",
which reminds of g_str_hash() and follows the pattern of g_str_equal().
Thus:

  g_hash_table_new(nm_str_hash, g_str_equal);

is preferable over

  g_hash_table_new(nm_hash_str, g_str_equal);

Hence, we have (and had) nm_str_hash() effectively an alias to
nm_hash_str.

The question is: which name is preferable? Or should they be both present
for their slightly distinct uses? The approach taken here is to have
both names, to reflect their purpose better.

But as the usage of nm_str_hash is as function pointer for GHashTable, it was
not an inline function and we'd pay a small overhead with this approach of
aliasing. Avoid that overhead by defining nm_str_hash with the C
preprocessor.

For similar reasons, do that for nm_direct_hash.

src/libnm-glib-aux/nm-hash-utils.c

@@ -138,12 +138,6 @@ nm_hash_str(const char *str)
     return nm_hash_complete(&h);
 }
 
-guint
-nm_str_hash(gconstpointer str)
-{
-    return nm_hash_str(str);
-}
-
 guint
 nm_hash_ptr(gconstpointer ptr)
 {
@@ -156,12 +150,6 @@ nm_hash_ptr(gconstpointer ptr)
     return nm_hash_complete(&h);
 }
 
-guint
-nm_direct_hash(gconstpointer ptr)
-{
-    return nm_hash_ptr(ptr);
-}
-
 /*****************************************************************************/
 
 guint

src/libnm-glib-aux/nm-hash-utils.h

@@ -201,10 +201,10 @@ nm_hash_update_str(NMHashState *state, const char *str)
 #endif
 
 guint nm_hash_ptr(gconstpointer ptr);
-guint nm_direct_hash(gconstpointer str);
+#define nm_direct_hash nm_hash_ptr
 
 guint nm_hash_str(const char *str);
-guint nm_str_hash(gconstpointer str);
+#define nm_str_hash ((guint(*)(gconstpointer str)) nm_hash_str)
 
 #define nm_hash_val(static_seed, val)     \
     ({                                    \