mptcp: drop MPTCP_ADDR_IPVERSION_4/6

Since the type of the address family in struct mptcp_options_received
became sa_family_t, we should set AF_INET/AF_INET6 to it, instead of
using MPTCP_ADDR_IPVERSION_4/6.

Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>