tcp: double default TSQ output bytes limit

tcp: double default TSQ output bytes limit

Xen virtual network driver has higher latency than a physical NIC.
Having only 128K as limit for TSQ introduced 30% regression in guest
throughput.

This patch raises the limit to 256K. This reduces the regression to 8%.
This buys us more time to work out a proper solution in the long run.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit c39c4c6abb89d24454b63798ccbae12b538206a5)
Oracle-Bug: 25424818
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Tested-by: Raj Matharasi <raj.matharasi@oracle.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>