Add --disable-detection configure option

Add --disable-detection configure option to compile Suricata with
detection disabled.

configure.ac

@@ -392,6 +392,13 @@
     ])
     AM_CONDITIONAL([HAVE_COCCINELLE], [test "x$enable_coccinelle" != "xno"])
 
+  # disable detection
+    AC_ARG_ENABLE(detection,
+           AS_HELP_STRING([--disable-detection], [Disable Detection Modules])], [enable_detection="$enableval"],[enable_detection=yes])
+    AS_IF([test "x$enable_detection" = "xno"], [
+        AC_DEFINE([HAVE_DETECT_DISABLED], [1], [Detection is disabled])]
+    ])
+
 # libraries
 
     AC_MSG_CHECKING([for Mpipe])
@@ -1631,6 +1638,7 @@ SURICATA_BUILD_CONF="Suricata Configuration:
   DAG enabled:                             ${enable_dag}
   Napatech enabled:                        ${enable_napatech}
   Unix socket enabled:                     ${enable_unixsocket}
+  Detection enabled:                       ${enable_detection}
 
   libnss support:                          ${enable_nss}
   libnspr support:                         ${enable_nspr}

src/suricata.c

@@ -927,7 +927,11 @@ static void SCInstanceInit(SCInstance *suri)
     suri->verbose = 0;
     /* use -1 as unknown */
     suri->checksum_validation = -1;
-    suri->disabled_detect = 0;
+#if HAVE_DETECT_DISABLED==1
+    g_detect_disabled = suri->disabled_detect = 1;
+#else
+    g_detect_disabled = suri->disabled_detect = 0;
+#endif
 }
 
 static TmEcode PrintVersion()