make shell math operations style more succulent

Convert the style:
	var=$((${var} + 1))
to:
	: $(( var += 1 ))

The latter is easier to read imo.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

net/ifconfig.sh.Linux.in

@@ -26,7 +26,7 @@ _ifindex()
 {
 	local line= i=-2
 	while read line; do
-		i=$((${i} + 1))
+		: $(( i += 1 ))
 		[ ${i} -lt 1 ] && continue
 		case "${line}" in
 			"${IFACE}:"*) echo "${i}"; return 0;;
@@ -34,7 +34,7 @@ _ifindex()
 	done < /proc/net/dev
 
 	# Return the next available index
-	i=$((${i} + 1))
+	: $(( i += 1 ))
 	echo "${i}"
 	return 1
 }
@@ -96,7 +96,7 @@ _get_inet_addresses()
 		_exists || break
 		local addr="$(_get_inet_address)"
 		[ -n "${addr}" ] && addrs="${addrs}${addrs:+ }${addr}"
-		i=$((${i} + 1))
+		: $(( i += 1 ))
 	done
 	echo "${addrs}"
 }
@@ -106,26 +106,26 @@ _cidr2netmask()
 	local cidr="$1" netmask="" done=0 i=0 sum=0 cur=128
 	local octets= frac=
 
-	local octets=$((${cidr} / 8))
-	local frac=$((${cidr} % 8))
+	local octets=$(( cidr / 8 ))
+	local frac=$(( cidr % 8 ))
 	while [ ${octets} -gt 0 ]; do
 		netmask="${netmask}.255"
-		octets=$((${octets} - 1))
-		done=$((${done} + 1))
+		: $(( octets -= 1 ))
+		: $(( done += 1 ))
 	done
 
 	if [ ${done} -lt 4 ]; then
 		while [ ${i} -lt ${frac} ]; do
-			sum=$((${sum} + ${cur}))
-			cur=$((${cur} / 2))
-			i=$((${i} + 1))
+			: $(( sum += cur ))
+			: $(( cur /= 2 ))
+			: $(( i += 1 ))
 		done
 		netmask="${netmask}.${sum}"
-		done=$((${done} + 1))
+		: $(( done += 1 ))
 
 		while [ ${done} -lt 4 ]; do
 			netmask="${netmask}.0"
-			done=$((${done} + 1))
+			: $(( done += 1 ))
 		done
 	fi
 
@@ -150,7 +150,7 @@ _add_address()
 		# Get the last alias made for the interface and add 1 to it
 		i=$(ifconfig | sed '1!G;h;$!d' | grep -m 1 -o "^${iface}:[0-9]*" \
 			| sed -n -e 's/'"${iface}"'://p')
-		i=$((${i:-0} + 1))
+		: $(( i = ${i:-0} + 1 ))
 		iface="${iface}:${i}"
 	fi