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

doc/health.md

@@ -14,6 +14,7 @@ rx   max 00 slow 0x0000
 tx   max 00 slow 0x0000
 stp  max 04 slow 0x0001
 cmd  max 02 slow 0x0001
+lldp max 00 slow 0x0000
 sp 80 untouched 62
 tcp st 00 tmr 00 rtx 00 rto 00 len 0x0000 mss 0x05b4
   lport 0x0000 rport 0x0000 rip 0x0000 0x0000
@@ -46,7 +47,7 @@ a flooded CPU port from a stalled loop, which look identical from outside.
 ## Phases
 
 Each line is one section of the main loop: the link poll, SFP handling,
-frame reception, TCP transmission, the STP timers and the command dispatch.
+frame reception, TCP transmission, the STP timers, the LLDP timer and the command dispatch.
 `max` is the worst time that section has taken, in ticks of 5 ms; `slow`
 counts the passes that took two ticks or more. A misbehaving subsystem
 names itself here, which is the difference between knowing that the loop is