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.