server session CHANGE make ps poll transport-specific

This means it must be active polling, but should
be always reliable.

Fixes cesnet/netopeer2#14
diff --git a/src/session_server.h b/src/session_server.h
index eff619a..dc0e556 100644
--- a/src/session_server.h
+++ b/src/session_server.h
@@ -234,12 +234,11 @@
 #define NC_PSPOLL_REPLY_ERROR 0x0008   /**< Response to the RPC was a \<rpc-reply\> of type error. */
 #define NC_PSPOLL_SESSION_TERM 0x0010  /**< Some session was terminated. */
 #define NC_PSPOLL_SESSION_ERROR 0x0020 /**< Some session was terminated incorrectly (not by a \<close-session\> or \<kill-session\> RPC). */
-#define NC_PSPOLL_PENDING 0x0040       /**< Unhandled pending events on other session. */
-#define NC_PSPOLL_ERROR 0x0080         /**< Other fatal errors (they are printed). */
+#define NC_PSPOLL_ERROR 0x0040         /**< Other fatal errors (they are printed). */
 
 #ifdef NC_ENABLED_SSH
-#   define NC_PSPOLL_SSH_MSG 0x0100       /**< SSH message received (and processed, if relevant, only with SSH support). */
-#   define NC_PSPOLL_SSH_CHANNEL 0x0200   /**< New SSH channel opened on an existing session (only with SSH support). */
+#   define NC_PSPOLL_SSH_MSG 0x0080       /**< SSH message received (and processed, if relevant, only with SSH support). */
+#   define NC_PSPOLL_SSH_CHANNEL 0x0100   /**< New SSH channel opened on an existing session (only with SSH support). */
 #endif
 
 /**