[CLEANUP] proxy: rename a few proxy states (PR_STIDLE and PR_STRUN)

Those states have been replaced with PR_STFULL and PR_STREADY respectively,
as it is what matches them the best now. Also, two occurrences of PR_STIDLE
in peers.c have been removed as this did not provide any form of error recovery
anyway.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 9bda578..e5d49ed 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -49,12 +49,14 @@
 #include <types/stick_table.h>
 
 /* values for proxy->state */
-#define PR_STNEW        0
-#define PR_STIDLE       1
-#define PR_STRUN        2
-#define PR_STSTOPPED    3
-#define PR_STPAUSED     4
-#define PR_STERROR      5
+enum {
+	PR_STNEW = 0,           /* proxy has not been initialized yet */
+	PR_STREADY,             /* proxy has been initialized and is ready */
+	PR_STFULL,              /* frontend is full (maxconn reached) */
+	PR_STPAUSED,            /* frontend is paused (during hot restart) */
+	PR_STSTOPPED,           /* proxy is stopped (end of a restart) */
+	PR_STERROR,             /* proxy experienced an unrecoverable error */
+};
 
 /* values for proxy->mode */
 #define PR_MODE_TCP     0