decode/erspan: Warn on ERSPAN Type I config

This commit checks whether pre-6.x settings for ERSPAN Type I are
present. ERSPAN Type I is no longer enabled/disabled through a
configuration setting -- it's always enabled.

When a setting exists to enable/disable ERSPAN Type I decoding, a
warning message is logged.

Enabling/disabling ERSPAN Type I decode has been deprecated in 6.x

src/decode-erspan.c

@@ -43,6 +43,21 @@
  * \brief Functions to decode ERSPAN Type I and II packets
  */
 
+/*
+ * \brief ERSPAN Type I was configurable in 5.0.x but is no longer configurable.
+ *
+ * Issue a warning if a configuration setting is found.
+ */
+void DecodeERSPANConfig(void)
+{
+    int enabled = 0;
+    if (ConfGetBool("decoder.erspan.typeI.enabled", &enabled) == 1) {
+        SCLogWarning(SC_WARN_ERSPAN_CONFIG,
+                     "ERSPAN Type I is no longer configurable and it is always"
+                     " enabled; ignoring configuration setting.");
+    }
+}
+
 /**
  * \brief ERSPAN Type I
  */

src/decode-erspan.h

@@ -34,4 +34,5 @@ typedef struct ErspanHdr_ {
     uint32_t padding;
 } __attribute__((__packed__)) ErspanHdr;
 
+void DecodeERSPANConfig(void);
 #endif /* __DECODE_ERSPAN_H__ */

src/decode.c

@@ -733,6 +733,7 @@ void DecodeGlobalConfig(void)
 {
     DecodeTeredoConfig();
     DecodeVXLANConfig();
+    DecodeERSPANConfig();
 }
 
 /**