When vfs.newnfs.callback_addr is set to an IPv4 address, the

experimental NFSv4 client might try and use it as an IPv6 address,
breaking callbacks. The fix simply initializes the isinet6 variable
for this case.

Approved by:	re (kensmith), kib (mentor)

sys/fs/nfsclient/nfs_clrpcops.c

@@ -753,7 +753,7 @@ nfsrpc_setclient(struct nfsmount *nmp, struct nfsclclient *clp,
 	nfsattrbit_t attrbits;
 	u_int8_t *cp = NULL, *cp2, addr[INET6_ADDRSTRLEN + 9];
 	u_short port;
-	int error, isinet6, callblen;
+	int error, isinet6 = 0, callblen;
 	nfsquad_t confirm;
 	u_int32_t lease;
 	static u_int32_t rev = 0;