wg-quick: linux: use sed for splitting config lines

Bash's longest matching operators combined with extended globs is
extremely slow for very large lines. There are probably very few people
for which this is noticable but in a file with 800 AllowIPs on a single
line it keeps wg-quick from stalling for 5s when performing operations.

src/wg-quick/linux.bash

@@ -49,8 +49,8 @@ parse_options() {
 	shopt -s nocasematch
 	while read -r line || [[ -n $line ]]; do
 		stripped="${line%%\#*}"
-		key="${stripped%%=*}"; key="${key##*([[:space:]])}"; key="${key%%*([[:space:]])}"
-		value="${stripped#*=}"; value="${value##*([[:space:]])}"; value="${value%%*([[:space:]])}"
+		key=$(sed -e 's/=.*$//' -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//' <<< "$stripped")
+		value=$(sed -e 's/^[^=]*=//' -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//' <<< "$stripped")
 		[[ $key == "["* ]] && interface_section=0
 		[[ $key == "[Interface]" ]] && interface_section=1
 		if [[ $interface_section -eq 1 ]]; then