nwbind: implement additional broadcast message calls

Add the missing NCP 21 message service endpoints for disabling/enabling
broadcast reception and for the newer send/get broadcast message calls.

Track a per-connection broadcast_disabled flag and use a shared helper for
storing pending broadcast messages and notifying the target nwconn process.
The old NCP 21/00 send path now uses the same helper as the newer NCP 21/10
path.

Also improve UNKNOWN FUNCTION logging in nwconn.c by including the NCP type,
function and, where available, subfunction. This makes future missing-endpoint
logs easier to map back to SDK/NCP documentation.

Based on the existing MARS-NWE message handling, the old lwared broadcast
implementation, and the Novell WebSDK message service layouts.

include/nwbind.h

@@ -37,6 +37,7 @@ typedef struct {
    uint8       crypt_key[8];    /* password generation   */
    time_t      t_login;         /* login time            */
    uint8       message[60];     /* saved BCastmessage    */
+   int         broadcast_disabled; /* client refuses messages */
    int         active;          /* 0=closed, 1= active   */
    int         send_to_sock;    /* this is the receiving sock */
    int         pid_nwconn;      /* pid of user process nwconn */