pam UPDATE auth using Linux PAM

Added the ability to authenticate via Linux PAM when using keyboard-interactive SSH authentication method. One new API call was added.
diff --git a/src/session_p.h b/src/session_p.h
index 916e235..b1224ef 100644
--- a/src/session_p.h
+++ b/src/session_p.h
@@ -195,6 +195,8 @@
     int (*interactive_auth_clb)(const struct nc_session *session, ssh_message msg, void *user_data);
     void *interactive_auth_data;
     void (*interactive_auth_data_free)(void *data);
+    char *conf_name;
+    char *conf_dir;
 #endif
 #ifdef NC_ENABLED_TLS
     int (*user_verify_clb)(const struct nc_session *session);
@@ -514,6 +516,18 @@
     void (*notif_clb)(struct nc_session *session, const struct lyd_node *envp, const struct lyd_node *op);
 };
 
+#ifdef NC_ENABLED_SSH
+
+/**
+ * @brief PAM callback arguments.
+ */
+struct nc_pam_thread_arg {
+    ssh_message msg;            /**< libssh message */
+    struct nc_session *session; /**< NETCONF session */
+};
+
+#endif
+
 void *nc_realloc(void *ptr, size_t size);
 
 struct passwd *nc_getpwuid(uid_t uid, struct passwd *pwd_buf, char **buf, size_t *buf_size);