net: rds: exchange of 8K and 1M pool

Before the commit 490ea596 ("RDS: IB: move FMR code to its own file"),
when the dirty_count is greater than 9/10 of max_items of 8K pool,
1M pool is used, Vice versa. After the commit 490ea596 ("RDS: IB: move
FMR code to its own file"), the above is removed. When we make the
following tests.

Server:
  rds-stress -r 1.1.1.16 -D 1M

Client:
  rds-stress -r 1.1.1.14 -s 1.1.1.16 -D 1M

The following will appear.
"
connecting to 1.1.1.16:4000
negotiated options, tasks will start in 2 seconds
Starting up..header from 1.1.1.166:4001 to id 4001 bogus
..
tsks  tx/s  rx/s tx+rx K/s  mbi K/s  mbo K/s tx us/c  rtt us
cpu %
   1    0    0     0.00     0.00     0.00    0.00 0.00 -1.00
   1    0    0     0.00     0.00     0.00    0.00 0.00 -1.00
   1    0    0     0.00     0.00     0.00    0.00 0.00 -1.00
   1    0    0     0.00     0.00     0.00    0.00 0.00 -1.00
   1    0    0     0.00     0.00     0.00    0.00 0.00 -1.00
...
"
So this exchange between 8K and 1M pool is added back.

Fixes: commit 490ea596 ("RDS: IB: move FMR code to its own file")
Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>