zebra: deal with irdp compile warnings

* zebra/irdp.h
  * irdp_send_thread(): move prototype to common header file
  * irdp_advert_off(): idem
  * process_solicit(): idem
  * irdp_read_raw(): idem
  * send_packet(): idem
* zebra/irdp_interface.c
  * inet_2a(): move function to where it is used
  * in_cksum(): lib/checksum.h already provides prototype
  * irdp_send_thread(): prototype moved away
  * inet_2a(): idem
  * irdp_advert_off(): idem
  * b1, b2, b3, b4: get rid of global buffers for inet_2a()
  * if_group(): add local buffer for inet_2a()
  * if_add_group(): idem
  * if_drop_group(): idem
  * irdp_config_write(): idem
  * Adv_new(): make static
* zebra/irdp_main.c
  * irdp_read_raw(): prototype moved away
  * send_packet(): idem
  * in_cksum(): lib/checksum.h already provides prototype
  * inet_2a(): function moved to irdp_interface.c
* zebra/irdp_packet.c
  * b1, b2, b3, b4: get rid of global buffers for inet_2a()
  * in_cksum(): lib/checksum.h already provides prototype
  * process_solicit(): prototype moved away
  * irdp_read_raw(): fix uninitialized variable
diff --git a/zebra/irdp.h b/zebra/irdp.h
index 1f0c1ec..9ce55e5 100644
--- a/zebra/irdp.h
+++ b/zebra/irdp.h
@@ -146,5 +146,12 @@
 extern int irdp_sock_init(void);
 extern void irdp_finish(void);
 extern void irdp_config_write (struct vty *, struct interface *);
+extern int irdp_send_thread(struct thread *t_advert);
+extern void irdp_advert_off(struct interface *ifp);
+extern void process_solicit (struct interface *ifp);
+extern int irdp_read_raw(struct thread *r);
+extern void send_packet(struct interface *ifp, struct stream *s,
+			u_int32_t dst, struct prefix *p, u_int32_t ttl);
+
 
 #endif /* _IRDP_H */