SCTP: Fix SCTP_SET_PEER_PRIMARY_ADDR to accpet v4mapped address

SCTP_SET_PEER_PRIMARY_ADDR does not accpet v4mapped address, using
v4mapped address in SCTP_SET_PEER_PRIMARY_ADDR socket option will
get -EADDRNOTAVAIL error if v4map is enabled. This patch try to
fix it by mapping v4mapped address to v4 address if allowed.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>