MINOR: checks: Export the tcpcheck_eval_ret enum

This enum will be used to define custom function for tcp-check expect rules.
diff --git a/include/types/checks.h b/include/types/checks.h
index c44fe8e..2205633 100644
--- a/include/types/checks.h
+++ b/include/types/checks.h
@@ -246,6 +246,12 @@
 	};
 };
 
+enum tcpcheck_eval_ret {
+	TCPCHK_EVAL_WAIT = 0,
+	TCPCHK_EVAL_STOP,
+	TCPCHK_EVAL_CONTINUE,
+};
+
 enum tcpcheck_expect_type {
 	TCPCHK_EXPECT_UNDEF = 0, /* Match is not used. */
 	TCPCHK_EXPECT_STRING, /* Matches a string. */
diff --git a/src/checks.c b/src/checks.c
index 6820d28..20280bd 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -2763,12 +2763,6 @@
 	return rule->index + 1;
 }
 
-enum tcpcheck_eval_ret {
-	TCPCHK_EVAL_WAIT = 0,
-	TCPCHK_EVAL_STOP,
-	TCPCHK_EVAL_CONTINUE,
-};
-
 /* Evaluate a TCPCHK_ACT_CONNECT rule. It returns 1 to evaluate the next rule, 0
  * to wait and -1 to stop the check. */
 static enum tcpcheck_eval_ret tcpcheck_eval_connect(struct check *check, struct tcpcheck_rule *rule)