Import dhcpcd-7.0.0-beta1

Summary of changes since dhcpcd-6.11.5:
  *  source file locations reworked:
       dhcpcd source is in src
       dhcpcd hooks are in hooks
       compat is in compat
  *  README split into README.md and BUILDING.md
  *  internal routing is now protocol agnostic
  *  avoid using __packed and use compile time asserts instead
  *  addresses some alignment issues
  *  disable some ARP code on kernels which support RFC5227
  *  BSD IPv6 kernel settings are now updated to reflect dhcpcd config
  *  custom logger has been removed, syslog handles everything
     as such, the --logfile option has been removed as well.
     If you need better/earlier logging, get a better syslogger!
  *  distinfo and signed distinfo files are now available alongside
     release taraballs from this point onwards
  *  default DBDIR has changed from /var/db to /var/db/dhcpcd
  *  /etc/dhcpcd.duid moves to DBDIR/duid
  *  /etc/dhcpcd.secret moves to DBDIR/secret
  *  lease file names have dhcpcd removed from them as they are now
     inside a directory of the same name
  *  fixed issues with reject routes not working on some platforms
  *  improved nl80211 support on Linux for working out the SSID
  *  no longer request NTP by default in dhcpcd.conf
  *  fix detecting IPv6 DAD on OpenBSD
  *  remove custom Solaris DLPI filtering in favour of BPF
     (note there seems to be a kernel issue where the DHCP
      fd receives ARP's as well, the only side effect is
      a noisy syslog)
  *  BPF filtering vastly improved so dhcpcd only wake up on
     ARP or DHCP packets destined for it
  *  support for MUD URL (draft-ietf-opsawg-mud-05)
  *  if the kernel isn't doing DAD, don't insist on waiting for it
     to actually do it
  *  fix a potential crash where the DHCP or ARP states could be
     freed before the packet processing loop naturally breaks
  *  removed gateway and nogateway options
     (these can be controlled by the nooption directive which
     works for more than just gateways)
  *  removed ipv6ra_own and ipv6ra_own_default options
     (these can be controled by the ipv6rs/noipv6rs directive)
  *  fix a memory leak on systems where posix_spawnattr_init
     allocates memory by calling posix_spawnattr_destroy afterwards
  *  fix a crash receiving SIGUSR1


(roy)