stream: use max-region setting from suricata.yaml

1. Add key (commented) to suricata.yaml
2. Give the configured/default key preference, save a check

src/util-streaming-buffer.c

@@ -213,7 +213,7 @@ static StreamingBufferRegion *FindRightEdge(const StreamingBufferConfig *cfg,
 static inline StreamingBufferRegion *InitBufferRegion(
         StreamingBuffer *sb, const StreamingBufferConfig *cfg, const uint32_t min_size)
 {
-    if (sb->regions == USHRT_MAX || (cfg->max_regions != 0 && sb->regions >= cfg->max_regions)) {
+    if ((cfg->max_regions != 0 && sb->regions >= cfg->max_regions) || (sb->regions == UINT16_MAX)) {
         SCLogDebug("max regions reached");
         sc_errno = SC_ELIMIT;
         return NULL;

suricata.yaml.in

@@ -1643,6 +1643,9 @@ flow-timeouts:
 #                               # is used or when stream-event:reassembly_overlap_different_data;
 #                               # is used in a rule.
 #
+#     max-regions: 8            # maximum number of concurrent regions per streaming buffer
+#                               # defaults to 8, if no configuration was provided. 0 means no limit.
+
 stream:
   memcap: 64 MiB
   #memcap-policy: ignore