MINOR: spoe: Replace sending_rate by a frequency counter

sending_rate was a counter used to evaluate the SPOE capacity to process
frames. Because it was not really accurrate, it has been replaced by a frequency
counter representing the number of frames handled by the SPOE per second. We
just check this counter is higher than the number of streams waiting for a
reply. If not, a new applet is created.
diff --git a/include/types/spoe.h b/include/types/spoe.h
index 3051056..2354f6e 100644
--- a/include/types/spoe.h
+++ b/include/types/spoe.h
@@ -262,7 +262,9 @@
 		unsigned int    frame_size;     /* current maximum frame size, only used to encode messages */
 		unsigned int    applets_act;    /* # of applets alive at a time */
 		unsigned int    applets_idle;   /* # of applets in the state SPOE_APPCTX_ST_IDLE */
-		unsigned int    sending_rate;   /* the global sending rate */
+
+		unsigned int    processing;
+		struct freq_ctr processing_per_sec;
 
 		struct freq_ctr conn_per_sec;   /* connections per second */
 		struct freq_ctr err_per_sec;    /* connetion errors per second */