[CLEANUP] stick_table: rename some stksess struct members to avoid confusion

The name 'exps' and 'keys' in struct stksess was confusing because it was
the same name as in the table which holds all of them, while they only hold
one node each. Remove the trailing 's' to more clearly identify who's who.
diff --git a/include/types/stick_table.h b/include/types/stick_table.h
index bbb9d0d..de23610 100644
--- a/include/types/stick_table.h
+++ b/include/types/stick_table.h
@@ -56,8 +56,8 @@
 struct stksess {
 	int sid;                  /* id of server to use for this session */
 	unsigned int expire;      /* session expiration date */
-	struct eb32_node exps;    /* ebtree node used to hold the session in expiration tree */
-	struct ebmb_node keys;    /* ebtree node used to hold the session in table */
+	struct eb32_node exp;     /* ebtree node used to hold the session in expiration tree */
+	struct ebmb_node key;     /* ebtree node used to hold the session in table */
 	/* WARNING! do not put anything after <keys>, it's used by the key */
 };