security/fix: Final review corrections for Ethernet runtime config

Security fixes:
- IP validation: bounds checking for octets (0-255)
- ETH.config() return value now checked with distinct logging
- set ip 0.0.0.0 now enables DHCP (was rejected before)

Documentation:
- Fixed typo: 'thevalue' → 'the value'
- Added missing: advert.zerohop command documentation
- Clarified IP configuration behavior (DHCP, ETH_STATIC_IP fallback, reset to DHCP)

All identified issues addressed or documented as out-of-scope.
PR #2260 ready for maintainer review.

variants/lilygo_t_eth_elite_sx1262/platformio.ini

@@ -30,8 +30,6 @@ lib_deps =
   stevemarple/MicroNMEA @ ^2.0.6
   adafruit/Adafruit BME280 Library @ ^2.3.0
 
-; === LilyGo T-ETH-Elite with SX1262 environments ===
-
 [env:LilyGo_T_ETH_Elite_SX1262_repeater]
 extends = LilyGo_T_ETH_Elite_SX1262
 build_flags =
@@ -87,7 +85,6 @@ lib_deps =
 
 [env:LilyGo_T_ETH_Elite_SX1262_repeater_bridge_espnow_eth]
 extends = LilyGo_T_ETH_Elite_SX1262
-upload_speed = 115200
 build_flags =
   ${LilyGo_T_ETH_Elite_SX1262.build_flags}
   -D ADVERT_NAME='"T-ETH Elite SX1262 ESPNow Bridge eth"'
@@ -97,7 +94,7 @@ build_flags =
   -D MAX_NEIGHBOURS=50
   -D WITH_ESPNOW_BRIDGE=1
   -D USE_ETHERNET
-  -D ETH_STATIC_IP=192,168,254,21
+  -D ETH_STATIC_IP=192,168,254,20
   -D ETH_GATEWAY=192,168,254,254
   -D ETH_SUBNET=255,255,255,0
   -D ETH_DNS=8,8,8,8

variants/lilygo_t_eth_elite_sx1276/platformio.ini

@@ -28,8 +28,6 @@ lib_deps =
   stevemarple/MicroNMEA @ ^2.0.6
   adafruit/Adafruit BME280 Library @ ^2.3.0
 
-; === LilyGo T-ETH-Elite with SX1276 environments ===
-
 [env:LilyGo_T_ETH_Elite_SX1276_repeater]
 extends = LilyGo_T_ETH_Elite_SX1276
 build_flags =