Log Message:
Import dhcpcd-5.5.4 with the following changes:
* ArchLinux SERVICESTATUS override fixed
* Shell portability fixes, including proper printf usage.
* Detect a valid ntp.conf before adjusting it
* Restart NTP correctly on Debian

* reboot timeout changed to 5 seconds
* When rebooting and not daemonized, reduce the discover timeout
  to allow for fallback or IPv4LL
* Respect each kernel carrier message
* Optimize some bitwise logic
* On Linux, pretent a bridge interface does not exist until IFF_LOWER_UP is set
* Don't remove interfaces for which commands have not been sent
* Store the assigned metric to each route so that we can change metrics on the fly
    dhcpcd -n --metric 100 iwi0
* Add SixRD support, RFC5969
* Fix SIP server support
* Only regen resolv.conf if it has changed
* Fix --reconfigure from spinning
* Add IPv6 Router Solicitation support we regards to RDNSS and DNSSL, RFC6016
* Add clang to the list of detected compilers
* Allow dhcpcd to run on a read only filesystem
* Don't attempt to tun the script if an empty string or /dev/null
* Stop truncating the netmask sockaddr on routing messages for BSD
* Prefer a DHCP lease over an IPv4LL one
* Fix carrier handling on BSD
* Fix arc4random detection on FreeBSD 7