mptcp: drop MPTCP_PM_MAX_ADDR

We have defined MPTCP_PM_ADDR_MAX in pm_netlink.c, so drop this duplicate macro.

Fixes: 1b1c7a0e ("mptcp: Add path manager interface")
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>