fix(health): give the LLDP phase a valid slot in the phase arrays

In HEALTH=1 builds health_phase(HEALTH_LLDP) used id 7 while ph_max[] and
ph_slow[] had HEALTH_PHASES = 6 entries. The LLDP checkpoint therefore
wrote one byte past ph_max (into the high byte of ph_slow[0]) and, when
the phase took two ticks or more, incremented two bytes past ph_slow
(dhcp_state.state and transaction_id on KP_9000_6XHML_X2).

Rename it HEALTH_PH_LLDP = 6, derive HEALTH_PHASES from it so the arrays
always cover the last phase, print an lldp line in "health" and document
it.

Fixes #658

cmd_parser.h

@@ -19,8 +19,8 @@ extern __xdata uint8_t err_status;
 #define HEALTH_PH_TX	3
 #define HEALTH_PH_STP	4
 #define HEALTH_PH_CMD	5
-#define HEALTH_PHASES	6
-#define HEALTH_LLDP     7
+#define HEALTH_PH_LLDP	6
+#define HEALTH_PHASES	(HEALTH_PH_LLDP + 1)	/* last id + 1: sizes the arrays in cmd_parser.c */
 
 extern __xdata uint16_t health_rx_frames;
 #define health_rx_frame()	health_rx_frames++