add udevmonitor, to debug netlink+udev events at the same time

add udevmonitor, to debug netlink+udev events at the same time

This rule:
  RUN+="socket:/org/kernel/udev/monitor"

send the event to the running monitor. Running udevstart give a nice
monitor output. Also the delay between the kernel uevent and the udev
udev event can be investigated:

  pim:/home/kay/src/udev-kay # ./udevmonitor
  UEVENT[1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1
  UEVENT[1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0
  UEVENT[1122920113] add@/class/scsi_host/host12
  UEVENT[1122920113] add@/class/usb_device/usbdev2.99
  UEVENT[1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0/host12/target12:0:0/12:0:0:0
  UDEV  [1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1
  UEVENT[1122920113] add@/block/sda
  UEVENT[1122920113] add@/class/scsi_generic/sg0
  UEVENT[1122920113] add@/class/scsi_device/12:0:0:0
  UDEV  [1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0
  UDEV  [1122920113] add@/class/scsi_host/host12
  UDEV  [1122920113] add@/class/usb_device/usbdev2.99
  UDEV  [1122920113] add@/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0/host12/target12:0:0/12:0:0:0
  UDEV  [1122920113] add@/block/sda
  UDEV  [1122920113] add@/class/scsi_generic/sg0
  UDEV  [1122920113] add@/class/scsi_device/12:0:0:0
  UEVENT[1122920115] add@/block/sda/sda1
  UDEV  [1122920115] add@/block/sda/sda1

  pim:/home/kay/src/udev-kay # ./udevmonitor --env
  UDEV  [1122920185] add@/block/sda/sda1
  ACTION=add
  DEVPATH=/block/sda/sda1
  SUBSYSTEM=block
  SEQNUM=2159
  MINOR=1
  MAJOR=8
  PHYSDEVPATH=/devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0/host13/target13:0:0/13:0:0:0
  PHYSDEVBUS=scsi
  PHYSDEVDRIVER=sd
  UDEVD_EVENT=1
  UDEV_LOG=3
  ID_VENDOR=IBM
  ID_MODEL=Memory_Key
  ID_REVISION=3.04
  ID_SERIAL=IBM_Memory_Key_0218B301030027E8
  ID_TYPE=disk
  ID_BUS=usb
  ID_PATH=usb-0218B301030027E8:0:0:0
  ID_FS_USAGE=filesystem
  ID_FS_TYPE=vfat
  ID_FS_VERSION=FAT16
  ID_FS_UUID=42D8-9E02
  ID_FS_LABEL_SAFE=s_p_c
  DEVNAME=/dev/sda1

Signed-off-by: Kay Sievers <kay.sievers@suse.de>