T8522: fix parse_icmp_attr() split delimiter and UnboundLocalError

• Use val.split("/") instead of val.split(".") when parsing type/code pairs
• In the numeric-only branch, use int(val) instead of the undefined type_no variable
• Cast both type and code to int for consistent typing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>