netlink: recover from netlink event socket errors (bsc#905421)
netlink: event socket and message buffer config (bsc#905421)

Allow to tune the netlink event socket buffer lengths adding:
  <netlink-events>
    <receive-buffer-length>...</receive-buffer-length>
    <message-buffer-length>...</message-buffer-length>
  </netlink-events>
to a <config> node in the /etc/wicked/local.xml.
Merge pull request #469 from mtomaschewski/rtnl-events

netlink: recover from netlink event socket errors