MEDIUM: stick-table: allocate the table key of size buffer size

Keys are copied from samples to stick_table_key. If a key is larger
than the stick_table_key, we have an overflow. In pratice it does not
happen because it requires :
   1) a configuration with tune.bufsize larger than BUFSIZE (common)
   2) a stick-table configured with keys strictly larger than buffers
   3) extraction of data larger than BUFSIZE (eg: using payload())

Points 2 and 3 don't make any sense for a real world configuration. That
said the issue needs be fixed. The solution consists in allocating it the
same size as the global buffer size, just like the samples. This fixes the
issue.
diff --git a/src/stick_table.c b/src/stick_table.c
index 75267e1..b681a8b 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -31,7 +31,7 @@
 #include <types/global.h>
 
 /* structure used to return a table key built from a sample */
-struct stktable_key static_table_key;
+struct stktable_key *static_table_key;
 
 /*
  * Free an allocated sticky session <ts>, and decrease sticky sessions counter
@@ -618,42 +618,42 @@
 	if (!sample_to_key[smp->type][t->type])
 		return NULL;
 
-	static_table_key.key_len = t->key_size;
-	static_table_key.key = sample_to_key[smp->type][t->type](smp, &static_table_key.data, &static_table_key.key_len);
+	static_table_key->key_len = t->key_size;
+	static_table_key->key = sample_to_key[smp->type][t->type](smp, &static_table_key->data, &static_table_key->key_len);
 
-	if (!static_table_key.key)
+	if (!static_table_key->key)
 		return NULL;
 
-	if (static_table_key.key_len == 0)
+	if (static_table_key->key_len == 0)
 		return NULL;
 
-	if ((static_table_key.key_len < t->key_size) && (t->type != STKTABLE_TYPE_STRING)) {
+	if ((static_table_key->key_len < t->key_size) && (t->type != STKTABLE_TYPE_STRING)) {
 		/* need padding with null */
 
 		/* assume static_table_key.key_len is less than sizeof(static_table_key.data.buf)
 		cause t->key_size is necessary less than sizeof(static_table_key.data) */
 
-		if ((char *)static_table_key.key > (char *)&static_table_key.data &&
-		    (char *)static_table_key.key <  (char *)&static_table_key.data + sizeof(static_table_key.data)) {
+		if ((char *)static_table_key->key > (char *)&static_table_key->data &&
+		    (char *)static_table_key->key <  (char *)&static_table_key->data + global.tune.bufsize) {
 			/* key buffer is part of the static_table_key private data buffer, but is not aligned */
 
-			if (sizeof(static_table_key.data) - ((char *)static_table_key.key - (char *)&static_table_key.data) < t->key_size) {
-				/* if not remain enougth place for padding , process a realign */
-				memmove(static_table_key.data.buf, static_table_key.key, static_table_key.key_len);
-				static_table_key.key = static_table_key.data.buf;
+			if (global.tune.bufsize - ((char *)static_table_key->key - (char *)&static_table_key->data) < t->key_size) {
+				/* if not remain enough place for padding , process a realign */
+				memmove(static_table_key->data.buf, static_table_key->key, static_table_key->key_len);
+				static_table_key->key = static_table_key->data.buf;
 			}
 		}
-		else if (static_table_key.key != static_table_key.data.buf) {
+		else if (static_table_key->key != static_table_key->data.buf) {
 			/* key definitly not part of the static_table_key private data buffer */
 
-			memcpy(static_table_key.data.buf, static_table_key.key, static_table_key.key_len);
-			static_table_key.key = static_table_key.data.buf;
+			memcpy(static_table_key->data.buf, static_table_key->key, static_table_key->key_len);
+			static_table_key->key = static_table_key->data.buf;
 		}
 
-		memset(static_table_key.key + static_table_key.key_len, 0, t->key_size - static_table_key.key_len);
+		memset(static_table_key->key + static_table_key->key_len, 0, t->key_size - static_table_key->key_len);
 	}
 
-	return &static_table_key;
+	return static_table_key;
 }
 
 /*