Please add DHCPv6 NTP options to stock dhcpcd.conf and exit hooks

[perkelix]

Our current stock config only features the IPv4 NTP server option (ntp_servers, 42, ipaddress). It doesn't any request IPv6 NTP option (sntp_servers, 00031, ip6address) or (ntp_server, 00056, ipv6address or FQDN).

Our config line should therefore be (subject to --enable-ntp uncommenting):

# Most distributions have NTP support (DHCP option 42, DHCPv6 options 31 and 56).
option ntp_servers, sntp_servers, ntp_server

Meanwhile our exit hooks only know about ntp_servers (IPv4) and sntp_servers (IPv6). However, they don't know anything about ntp_server (IPv6), which is somewhat problematic since it's the only NTP option that can receive an FQDN as the answer.

[rsmarples]

If you don't specify any DHCPv6 options then you get your DHCPv4 options mapped where applicable.
So NTP servers should be requested for DHCPv4 and DHCPv6 if you just uncomment the option in the default config.

[perkelix]

$ sudo dhcpcd --variables | grep ntp
042 ntp_servers                         	 array ipaddress
071 nntp_server                         	 array ipaddress
00031 sntp_servers                      	 array ip6address
00056 ntp_server                        	 encap

Based on this, one wouldn't know that uncommenting ntp_servers, in practice, requests both 042 and 00031. If that is the case, it needs to be documented.

It still leaves 00056 not covered by our exit hook.