Merge branch 'ipv6-next'

Hannes Frederic Sowa says:

====================
ipv6: cleanup after rt6_genid removal

Leftover patches after rt6_genid removal after 705f1c869d577c ("ipv6:
remove rt6i_genid").

Major two changes are:
* keep fib6_sernum per namespace to reduce number of flushes in case
  system has high number of namespaces
* make fn_sernum updates cheaper

v2: Incorporated feedback from Cong Wang, thanks a lot!
====================

Signed-off-by: David S. Miller <davem@davemloft.net>