isisd: API: area (L1), domain (L2) passwords

Last isisd CLI cleanup for now.  This also folds L1 & L2 configs into
common functions, reducing CLI function bloat by a bit.

(This patch contains changes authored by both Christian Franke and David
Lamparter.)

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/isisd/isisd.h b/isisd/isisd.h
index 0186644..eedb451 100644
--- a/isisd/isisd.h
+++ b/isisd/isisd.h
@@ -152,7 +152,12 @@
 			            uint16_t max_lsp_lifetime);
 void isis_area_lsp_refresh_set(struct isis_area *area, int level,
 			       uint16_t lsp_refresh);
-
+/* IS_LEVEL_1 sets area_passwd, IS_LEVEL_2 domain_passwd */
+int isis_area_passwd_unset (struct isis_area *area, int level);
+int isis_area_passwd_cleartext_set (struct isis_area *area, int level,
+                                    const char *passwd, u_char snp_auth);
+int isis_area_passwd_hmac_md5_set (struct isis_area *area, int level,
+                                   const char *passwd, u_char snp_auth);
 void isis_vty_init (void);
 
 /* Master of threads. */