sfp: do not block the main loop while a module wakes up

handle_sfp() called sfp_module_read() as soon as it saw a module appear, and
that path opened with delay(100). delay() spins on PCON until the tick counter
runs down, so the main loop stood still for 100 ticks - half a second at
SYS_TICK_HZ 200. Nothing else ran in that window: no STP, no LACP, no packet
handling. A diagnostic build measured the sfp phase at up to 107 ticks, the
longest stall of any phase in the loop.

Remember when the module showed up and let the loop continue. The I2C read
happens on a later pass, once the wake-up period has elapsed. Pulling a module
cancels a pending read, and a failed read still restores the detect bit, so the
existing retry-on-the-next-poll behaviour is unchanged.

The comparison is written out rather than using a helper so that this does not
depend on anything outside the current tree. The pending flag is an array
indexed by slot, like the other per-slot state in this file.

Cost on SWTGW218AS, measured against the branch point: BANK3 11173 -> 11264,
CSEG, BANK1 and BANK2 unchanged, plus 4 bytes of xdata.

sfp.h

@@ -1,6 +1,8 @@
 #ifndef SFP_H
 #define SFP_H
 
+#define SFP_WAKE_TICKS	100
+
 extern __xdata uint8_t sfp_pins_last;
 extern __xdata char sfp_module_vendor[2][17];
 extern __xdata char sfp_module_model[2][17];