From: Xin Long <lucien.xin@gmail.com>
Date: Sun, 18 Nov 2018 16:14:47 +0800

This reverts commit 22d7be267eaa8114dcc28d66c1c347f667d7878a.

The dst's mtu in transport can be updated by a non sctp place like
in xfrm where the MTU information didn't get synced between asoc,
transport and dst, so it is still needed to do the pmtu check
in sctp_packet_config.

Applied and queued up for -stable.

Please provide a proper signoff for reverts in the future.

Thanks.