netfilter: nf_tables: fix memory leak on error exit return

Currently the -EBUSY error return path is not free'ing resources
allocated earlier, leaving a memory leak. Fix this by exiting via the
error exit label err5 that performs the necessary resource clean
up.

Detected by CoverityScan, CID#1432975 ("Resource leak")

Fixes: 9744a6fcefcb ("netfilter: nf_tables: check if same extensions are set when adding elements")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -4080,8 +4080,10 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			if (nft_set_ext_exists(ext, NFT_SET_EXT_DATA) ^
 			    nft_set_ext_exists(ext2, NFT_SET_EXT_DATA) ||
 			    nft_set_ext_exists(ext, NFT_SET_EXT_OBJREF) ^
-			    nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF))
-				return -EBUSY;
+			    nft_set_ext_exists(ext2, NFT_SET_EXT_OBJREF)) {
+				err = -EBUSY;
+				goto err5;
+			}
 			if ((nft_set_ext_exists(ext, NFT_SET_EXT_DATA) &&
 			     nft_set_ext_exists(ext2, NFT_SET_EXT_DATA) &&
 			     memcmp(nft_set_ext_data(ext),