MEDIUM: checks: Add implicit tcp-check connect rule

After the configuration parsing, when its validity check, an implicit tcp-check
connect rule is added in front of the tcp-check ruleset if the first non-comment
rule is not a connect one. This implicit rule is flagged to use the default
check parameter.

This means now, all tcp-check rulesets begin with a connect and are never
empty. When tcp-check healthchecks are used, all connections are thus handled by
tcpcheck_main() function.
diff --git a/include/types/checks.h b/include/types/checks.h
index 2fc8012..521dca8 100644
--- a/include/types/checks.h
+++ b/include/types/checks.h
@@ -211,10 +211,11 @@
 	unsigned char lr[HANA_OBS_SIZE];	/* result for l4/l7: 0 = ignore, 1 - error, 2 - OK */
 };
 
-#define TCPCHK_OPT_NONE         0x0000  /* no options specified, default */
-#define TCPCHK_OPT_SEND_PROXY   0x0001  /* send proxy-protocol string */
-#define TCPCHK_OPT_SSL          0x0002  /* SSL connection */
-#define TCPCHK_OPT_LINGER       0x0004  /* Do not RST connection, let it linger */
+#define TCPCHK_OPT_NONE            0x0000  /* no options specified, default */
+#define TCPCHK_OPT_SEND_PROXY      0x0001  /* send proxy-protocol string */
+#define TCPCHK_OPT_SSL             0x0002  /* SSL connection */
+#define TCPCHK_OPT_LINGER          0x0004  /* Do not RST connection, let it linger */
+#define TCPCHK_OPT_DEFAULT_CONNECT 0x0008  /* Do a connect using server params */
 
 struct tcpcheck_connect {
 	uint16_t port; /* port to connect to */