fm10k: change default Tx ITR to 25usec

The current default ITR for Tx is overly restrictive. Using a simple
netperf TCP_STREAM test, we top out at about 10Gb/s for a single thread
when running using 1500 byte frames. By reducing the ITR value to 25usec
(up to 40K interrupts a second from 10K), we are able to achieve 36Gb/s
for a single thread TCP stream test.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>