Merge branch 'noprefixroute'

Thomas Haller says:

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ipv6 addrconf: add IFA_F_NOPREFIXROUTE flag to suppress creation of IP6 routes

v1 -> v2: add a second commit, handling NOPREFIXROUTE in ip6_del_addr.
v2 -> v3: reword commit messages, code comments and some refactoring.
v3 -> v4: refactor, rename variables, add enum
v4 -> v5: rebase, so that patch applies cleanly to current net-next/master
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Signed-off-by: David S. Miller <davem@davemloft.net>