Merge pull request #14 from dedeckeh/bugfixes

Fix DHCPv6 relay reply message in case raw DHCPv6 attributes are present
Fix DHCP settings for /28
dhcpv4: use search domain instead of domain option
config: accept domains with trailing .
Fix option id for hostnames
dhcpv4: update hostfile more often
add more consistency to host file writing
dhcpv6: send NotOnLink status on global level
Make hostid more convenient
backup for notonlink
use leaetime as base for T1 and T2 upper bound
Fix DHCPv4 static leases (thanks arnd)
Fixes compile error with musl

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
leasefile: do not output expired dhcpv6 leases

Sometimes ip that is assigned to a host changes, old ip is still kept aroung as 'expired'.
This expired ip gets dumped into leasefile and is read by dnsmasq.
The result is that hotsname is resolved into expired ip and that confuses clients.
This patch prevents expired leases from being written into leasefile.
Merge pull request #17 from mar-kolya/master

leasefile: do not output expired dhcpv6 leases
DHCPv4: send DHCPNAK if requested addr != leased addr
DHCPv6 destination address check

As described in RFC3315 §15 any solicit, confirm, rebind or information request message is discarded if the destination address is unicast
Likewise any request (§18.2.1), renew (§18.2.3), release (§18.2.6) or decline (§18.2.7) message is discarded and the server replies with the status code use multicast.
Replace option sol_max_rt by inf_max_rt in reply response to information request