net: ipv6: Generate all random IID for addresses on RAWIP devices

This reverts commit 557a3b4d ("net: ipv6: Generate random IID
for addresses on RAWIP devices") and commit 8601ea92 ("ipv6: Do
not generate random IID only for RAWIP devices").

This scheme allows for generation of a new IID each time the
interface state is toggled rather than it persisting for the
lifetime of the device.

CRs-Fixed: 2379253
Change-Id: I5c524ae18c374e3afcc26b4ba93a292d51839ed1
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>