spa: add spa_alloca that does overflow and limit checks

Make a function like alloca but with overflow checks and a max
allocation size.

Use this function where we can and also make sure that all alloca calls
are in some way limited.

src/modules/module-protocol-pulse/defs.h

@@ -34,6 +34,9 @@
 
 #define MAXLENGTH		(4u*1024*1024) /* 4MB */
 
+/* pulseaudio has a 128 char limit for this but we can allow more */
+#define MAX_NAME		1024u
+
 #define SCACHE_ENTRY_SIZE_MAX	(1024*1024*16)
 
 #define MODULE_INDEX_MASK	0xfffffffu