hf mf sim: reduce 6ms threshold to 4ms for reset to idle

Fixes some readers not being able to detect the simulated card on
second Inventory command due to the RF field being powered off for
a short time before being turned on again to reset the card to idle
state.

Closes #1974

CHANGELOG.md

@@ -3,6 +3,7 @@ All notable changes to this project will be documented in this file.
 This project uses the changelog in accordance with [keepchangelog](http://keepachangelog.com/). Please use this to write notable changes, which is not the same as git commit log...
 
 ## [unreleased][unreleased]
+ - Changed `hf mf sim` - reduce 6ms threshold to 4ms for reset to idle #1974 (@net147)
  - Rebuilt the Spartan-2 `fpga_*.bit` files to include the `hi_iso14443a.v` update (@d18c7db)
  - Added minor orphaned change from `hi_iso14443a.v` in `fpga-xc3s100e` to `hi_iso14443a.v` in `fpga-xc2s30` (@d18c7db)
  - Added python3 script to convert amiibo nfc Flipper Zero files to eml files to be used with Proxmark3 (@OscarAkaElvis)

armsrc/iso14443a.c

@@ -2084,8 +2084,8 @@ int EmGetCmd(uint8_t *received, uint16_t *len, uint8_t *par) {
                     if (timer == 0) {
                         timer = GetTickCount();
                     } else {
-                        // 6ms no field --> card to idle state
-                        if (GetTickCountDelta(timer) > 6) {
+                        // 4ms no field --> card to idle state
+                        if (GetTickCountDelta(timer) > 4) {
                             return 2;
                         }
                     }