Merge branch 'documentation-add-description-for-a-couple-of-sctp-sysctl-options'

Xin Long says:

====================
Documentation: add description for a couple of sctp sysctl options

These are a couple of sysctl options I recently added, but missed adding
documents for them. Especially for net.sctp.intl_enable, it's hard for
users to setup stream interleaving, as it also needs to call some socket
options.

This patchset is to add documents for them.
====================

Link: https://lore.kernel.org/r/cover.1654787716.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>