dhcp4: don't use offered address in initial request

Do not send initial request using the offered IP address as source
address or server address in destination, but broadcast on layer 2
and 3 (RFC 2131, Section 3.1.3).
dhcp4: set fsm state before building the message

The state is required to distinguish e.g. between different request
types while building the message, not only to handle responses.
Merge pull request #12 from mtomaschewski/dhcp-request-1

dhcp4 request fixes 1
remove TODO file, moved to individual github issues
Remove newline from debug output in __ni_config_parse_ifconfig_source
Merge pull request #85 from olafhering/tweak_todo_list
Merge pull request #86 from olafhering/ni_config_parse_ifconfig_source-newline
Readded a TODO referencing github issues
dhcp6: fixed to accept low preference server offers

We wait until retransmit timeout before we accept
offers from low preference servers.
We may make it configurable how long to wait later.
Log and return error from nl_send_auto
Return -NLE_NOMEM if __ni_nl_cb_clone fails
Make __ni_nl_talk static
Print libnl errors from ni_nl_talk
Catch libnl errors in __ni_dcb_getdcb
Print errors from nl_recvmsgs only in debug mode
Merge pull request #87 from mtomaschewski/dhcp-request-2

dhcp6: fixed to accept low preference server offers
Merge pull request #88 from olafhering/olh_ni_nl_talk_error_handling
Replace hardcoded array sizes in lldp.c
Handle calloc failure in ni_capture_open
Update ni_capture_free to handle NULL pointer