Preserve IFS in __stop_legacy_networking (#366)

__stop_legacy_networking sets IFS to ',' without restoring it. This
confuses subsequent variable expansions in the function and does not
release IPv6 resources for jails with multiple IPv6 aliases.

(cherry picked from commit 9cf580d)

lib/ioc-network

@@ -222,6 +222,7 @@ __stop_legacy_networking () {
     ip6_addr=$(echo $ip6_addr | sed "s/DEFAULT|/$default_iface|/g")
 
     if [ "$ip4_addr" != "none" ] ; then
+        local oIFS=$IFS
         local IFS=','
         for ip in $ip4_addr ; do
             local iface="$(echo $ip | \
@@ -232,9 +233,11 @@ __stop_legacy_networking () {
 
             ifconfig $iface $ip4 -alias
         done
+        local IFS=$oIFS
     fi
 
     if [ "$ip6_addr" != "none" ] ; then
+        local oIFS=$IFS
         local IFS=','
         for ip6 in $ip6_addr ; do
             local iface="$(echo $ip6 | \
@@ -244,5 +247,6 @@ __stop_legacy_networking () {
                        awk 'BEGIN { FS = "/" } ; { print $1 }')"
             ifconfig $iface inet6 $ip6 -alias
         done
+        local IFS=$oIFS
     fi
 }