Simplify notification code in NetlinkHandler.

1. Factor most of the notification code out to a common function.
2. Use vasprintf instead of snprintf so we don't have to worry
   about clipping notifications due to fixed-size message
   buffers.

Bug: 9180552
Change-Id: Idde16ee6dd56d38dab866f0ea678b04d98b3048d
2 files changed