inet:ipv6: Fixed generation of IPv6 IID for RAW_IP devices.

The kernel is generating a new IPv6 IID each time a new Router
Advertisement message is received for RAW_IP devices.

This change uses an already generated IID, if one exists.

Change-Id: Iebfbfd6707a7b552d49b4b74e4717b400d29d647
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Merge "inet:ipv6: Fixed generation of IPv6 IID for RAW_IP devices." into android-msm-2.6.32