Merge pull request #18 from dedeckeh/bugfixes

Improved compliance with RFC3315
odhcpd: only enable packet socket if really needed
Initial rewrite of NDP proxy
Add missing NDP sync features
Fix compilation
Fix typo in ubus integration
Revert "rewrite of NDP proxy" for now
Don't loose routes in managed PD
ra: don't send MSR for /64 prefix if DP is /64 as well
sync hostfile more often
Add host-entries for all IPv6 addresses
Make failed to send a notice instead of a warning
dhcpv4: log requests and replies to syslog

This change let odhcpd print dhcpv4 events
to syslog.
dhcpv4: implement router configuration option

RFC 2132 defines:

3.5. Router Option

   The router option specifies a list of IP addresses for routers on the
   client's subnet.  Routers SHOULD be listed in order of preference.

   The code for the router option is 3.  The minimum length for the
   router option is 4 octets, and the length MUST always be a multiple
   of 4.

    Code   Len         Address 1               Address 2
   +-----+-----+-----+-----+-----+-----+-----+-----+--
   |  3  |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  ...
   +-----+-----+-----+-----+-----+-----+-----+-----+--
Merge pull request #20 from mehlis/implement-dhcp4-router-config

dhcpv4: implement router configuration option
dhcpv4: offer a valid configuration with DHCP NAK

On network change the client requests a non valid
configuration. In this case we have to reply with
a DHCP NAK. But this NAK can include a valid
configuration like an ACK does.

With this change iDevices and Androids can finish
DHCP even with wrong configuration in first
REQUEST with two packets and without any additional
timeouts and round trips.
Merge pull request #21 from mehlis/fix-nak-by-doing-valid-reply

dhcpv4: offer a valid configuration with DHCP NAK
Merge pull request #22 from mehlis/log-dhcp4-events

dhcpv4: log requests and replies to syslog
PD: don't consider deprecated assigned prefixes when calculating avilable PD size
dhcpv4: added more comments