Overhaul dhcpcd for chrome os use

dhcpcd-hooks/50-yp.conf

-# Sample dhcpcd hook for ypbind
-# This script is only suitable for the Linux version.
-
-ypbind_pid()
-{
-        [ -s /var/run/ypbind.pid ] && cat /var/run/ypbind.pid
-}
-
-make_yp_conf()
-{
-        [ -z "$new_nis_domain" -a -z "$new_nis_servers" ] && return 0
-        local cf=/etc/yp.conf."$interface" prefix= x= pid=
-        rm -f "$cf"
-        echo "$signature" > "$cf"
-        if [ -n "$new_nis_domain" ]; then
-                domainname "$new_nis_domain"
-                if [ -n "$new_nis_servers" ]; then
-                        prefix="domain $new_nis_domain server "
-                else
-                        echo "domain $new_nis_domain broadcast" >> "$cf"
-                fi
-        else
-                prefix="ypserver "
-        fi
-        for x in $new_nis_servers; do
-                echo "$prefix$x" >> "$cf"
-        done
-        save_conf /etc/yp.conf
-        cat "$cf" > /etc/yp.conf
-        rm -f "$cf"
-        pid="$(ypbind_pid)"
-        if [ -n "$pid" ]; then
-                kill -HUP "$pid"
-        fi
-}
-
-restore_yp_conf()
-{
-        [ -n "$old_nis_domain" ] && domainname ""
-        restore_conf /etc/yp.conf || return 0
-        local pid="$(ypbind_pid)"
-        if [ -n "$pid" ]; then
-                kill -HUP "$pid"
-        fi
-}
-
-case "$reason" in
-BOUND|INFORM|REBIND|REBOOT|RENEW|TIMEOUT|STATIC)        make_yp_conf;;
-EXPIRE|FAIL|IPV4LL|NAK|NOCARRIER|RELEASE|STOP)          restore_yp_conf;;
-esac