sctp: add support for generating stream reconf add incoming/outgoing streams request chunk

This patch is to define Add Incoming/Outgoing Streams Request
Parameter described in rfc6525 section 4.5 and 4.6. They can
be in one same chunk trunk as rfc6525 section 3.1-7 describes,
so make them in one function.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>