mptcp: Fix wrong comment about MPTCP_MAX_ADDR

Fix wrong comment about MPTCP_MAX_ADDR.

Depends-on: c62a1adb2a8f20 (Split mptcp_loc{4,6} into mptcp_loc{4,6} and mptcp_rem{4,6})
Signed-off-by: Kenjiro Nakayama <nakayamakenjiro@gmail.com>
Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>