MINOR: shctx: Add a maximum object size parameter.

This patch adds a new parameter to shctx_init() function to be used to
limit the size of each shared object, -1 value meaning "no limit".
diff --git a/src/cache.c b/src/cache.c
index a198b40..c0e8957 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -882,7 +882,7 @@
 			goto out;
 		}
 
-		ret_shctx = shctx_init(&shctx, tmp_cache_config->maxblocks, CACHE_BLOCKSIZE, sizeof(struct cache), 1);
+		ret_shctx = shctx_init(&shctx, tmp_cache_config->maxblocks, CACHE_BLOCKSIZE, -1, sizeof(struct cache), 1);
 
 		if (ret_shctx < 0) {
 			if (ret_shctx == SHCTX_E_INIT_LOCK)