odhcp6c: message retransmission count support

The patch implements message retransmission count (MRC) support as
described in RFC3315 paragraphs 5.5 and 14 for DHCPv6 request/release/
decline messages. Patch also disables multicast packets loopback.

Signed-off-by: Hans Dedecker <hans.dedecker@gmail.com>
odhcp6c: preference and status code support in advertise

The patch implements handling of advertise messages
as described in RFC3315 paragraph 17.1.2. Client will
stop collecting advertise messages if preference option
is equal to 255 or if the first RT has elapsed. Status
codes are handled in the advertise message depending on
the startup parameters

Signed-off-by: Hans Dedecker <hans.dedecker@gmail.com>
odhpc6c: status code support in reply

The patch implements support for status code handling in
reply messages as described in RFC3313 paragraph 18.1.8.
The client will
*log the status codes returned by the client
*send a request if no binding status code is returned for
a given IA
*send further renew/rebind if the IA was not present in
the reply
*terminate message exchange when no prefix/no address
status code is returned in reponse to a request
*terminate message exchange when unspec fail status code
is returned
*calculate t1/t2/t3 when all IA's have been processed and
based on recorded t1/t2/valid timer values per IA

Without this patch I have seen issues with request messages
send without any IA_PD/IA_NA and t1/t2/t3 timer values which
were not correct. These changes have been tested intensive
against an ISC DHCPv6 server

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