update structure of TcpInfo

The TCP infoamtion will be kept for evaluating data stall. The
memoery usage inside TST will increase based on the number of
TCP sockets exist in the device. For the evaluation, TST needs
only 4 fields from TcpInfo. The others are redundant currently.
Thus, keep only necessary field inside TcpInfo to reduce the
memory usgae.

Bug: 148115807
Test: atest NetworkStackTests NetworkStackNextTests
Test: manual test to check memory change
Change-Id: I35275f3d77bbf1e076f2fd327a961278fe038b63