net: rds: use correct size for max unacked packets and bytes

Max unacked packets/bytes is an int while sizeof(long) was used in the
sysctl table.

This means that when they were getting read we'd also leak kernel memory
to userspace along with the timeout values.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>