sctp: use KMALLOC_MAX_SIZE instead of its own MAX_KMALLOC_SIZE

Don't definite its own MAX_KMALLOC_SIZE, use the one
defined in mm.

Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>