dhcpv6: sanitize option request list

dhcpv6: sanitize option request list

By config statefull options can be specified for the option request
list which will be included in DHCPv6 INFORMATION request messages.
Obviously this is wrong as both RFC3315 and RFC8415 specify no
statefull options must be included in stateless mode.
In RFC8415 Table 4 specifies the options which can be included in
the option request list and which options are required to be requested
in some messages.
This commit extends the option table with flags indicating which options
may be included in the option request list.
On top the client adds by default the options 32/82/83 as they're
required to be sent depending on the message.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>