e1000: fix K1 configuration

This patch is for the following updates to the K1 configurations:
Tx idle period for entering K1 should be 128 ns.
Minimum Tx idle period in K1 should be 256 ns.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>

PR: 258153
Reviewed by: erj
Tested by: iron.udjin@gmail.com
Approved by: imp
Obtained from: DPDK (6f934fa24dfd437c90ead96bc7598ee77a117ede)
MFC after: 1 week