ipv6: generate random IID only for temporary addresses on RAWIP devices

RAWIP devices require the device IID to be used for permanent
addresses only, and random IIDs to be generated for temporary
addresses. Legacy user-space applications rely on this behavior

CRs-Fixed: 1078373
Change-Id: I007bdf8bcfdce687ad31612fed9d9c769321edb9
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>