sctp: fix some type cast warnings introduced by stream reconf

These warnings were found by running 'make C=2 M=net/sctp/'.

They are introduced by not aware of Endian when coding stream
reconf patches.

Since commit c0d8bab6 ("sctp: add get and set sockopt for
reconf_enable") enabled stream reconf feature for users, the
Fixes tag below would use it.

Fixes: c0d8bab6

 ("sctp: add get and set sockopt for reconf_enable")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>