pihole -d: Fix gateway ping if it is a LL address

[DL6ER]

What does this implement/fix?

Fix pinging the interface by appending the connected interface's identifier to the gateway address if it is a link-local address.

Before:

After:

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pihole-v6-debug-bug-found/67134/3

[yubiuser]

Do you extend the PR for the dig check at

pi-hole/advanced/Scripts/piholeDebug.sh

Lines 758 to 782 in 6e8029f

	addresses="$(ip address show dev "${iface}" | sed "/${sed_selector} /!d;s/^.*${sed_selector} //g;s/\/.*$//g;")"
	if [ -n "${addresses}" ]; then
	while IFS= read -r local_address ; do
	# Check if Pi-hole can use itself to block a domain
	if local_dig="$(dig +tries=1 +time=2 -"${protocol}" "${random_url}" @"${local_address}" "${record_type}")"; then
	# If it can, show success
	if [[ "${local_dig}" == *"status: NOERROR"* ]]; then
	local_dig="NOERROR"
	elif [[ "${local_dig}" == *"status: NXDOMAIN"* ]]; then
	local_dig="NXDOMAIN"
	else
	# Extract the first entry in the answer section from dig's output,
	# replacing any multiple spaces and tabs with a single space
	local_dig="$(echo "${local_dig}" | grep -A1 "ANSWER SECTION" | grep -v "ANSWER SECTION" | tr -s " \t" " ")"
	fi
	log_write "${TICK} ${random_url} ${COL_GREEN}is ${local_dig}${COL_NC} on ${COL_CYAN}${iface}${COL_NC} (${COL_CYAN}${local_address}${COL_NC})"
	else
	# Otherwise, show a failure
	log_write "${CROSS} ${COL_RED}Failed to resolve${COL_NC} ${random_url} on ${COL_RED}${iface}${COL_NC} (${COL_RED}${local_address}${COL_NC})"
	fi
	done <<< "${addresses}"
	else
	log_write "${TICK} No IPv${protocol} address available on ${COL_CYAN}${iface}${COL_NC}"
	fi
	done <<< "${interfaces}"

(Also reported on the linked Discourse post, second half of the intial post)

[DL6ER]

Added screenshots to the PR description