net: sctp: fix ASCONF to allow non SCTP_ADDR_SRC addresses in ipv6

Commit 8a07eb0a ("sctp: Add ASCONF operation on the single-homed host")
implemented possible use of IPv4 addresses with non SCTP_ADDR_SRC state
as source address when sending ASCONF (ADD) packets, but IPv6 part for
that was not implemented in 8a07eb0a. Therefore, as this is not restricted
to IPv4-only, fix this up to allow the same for IPv6 addresses in SCTP.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Michio Honda <micchie@sfc.wide.ad.jp>
Acked-by: Michio Honda <micchie@sfc.wide.ad.jp>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>