Merge branch 'ipv6-fixes-for-RTF_CACHE-entries'

Paolo Abeni says:

====================
ipv6: fixes for RTF_CACHE entries

This series addresses 2 different but related issues with RTF_CACHE
introduced by the recent refactory.

patch 1 restore the gc timer for such routes
patch 2 removes the aged out dst from the fib tree, properly coping with pMTU
routes

v1 -> v2:
 - dropped the  for ip route show cache
 - avoid touching dst.obsolete when the dst is aged out

v2 -> v3:
 - take care of pMTU exceptions
====================

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