Merge branch 'get_addr_rta' into iproute2-next

Serhey Popovych  says:

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Now we enhance get_addr() to return additional information about address
(e.g. if it unspecified or multicast) we want to have same functionality
for attributes in netlink message.

Introduce and use get_addr_rta() that parses given netlink attribute
into @inet_prefix data structure in the same way similar get_addr()
parses address from it's string representation.

Use attribute length to guess address family: force it by giving non
AF_UNSPEC @family to get_addr_rta() to ensure address is of expected
family.

Introduce and use inet_addr_match_rta() to further simplify and unify
code where get_addr_rta() intended to be used together with
inet_addr_match().

This is next step in ipv4 and ipv6 modules unification to prepare for
merge in the future.

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Signed-off-by: David Ahern <dsahern@gmail.com>