Squash-to: "selftests: mptcp: add testcase for active-back"

we need to use big-enough client file on link failure test.

We compute the expected link usage assuming half of the client
data will be sent after the link failure. The link failure
happens after sending once the client file, and than the client
file is sent again. After the link failure, a whole cwin amount
of data can be re-inected: to be able to predict correctly
the link utilization the client file size must be much greater
then max cwin.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -505,9 +505,13 @@ run_tests()
 	# create the input file for the failure test when
 	# the first failure test run
 	if [ "$test_linkfail" -ne 0 -a -z "$cinfail" ]; then
-		size=$((RANDOM%8))
+		# the client file must be considerably larger
+		# of the maximum expected cwin value, or the
+		# link utilization will be not predicable
+		size=$((RANDOM%2))
 		size=$((size+1))
-		size=$((size*2048))
+		size=$((size*8192))
+		size=$((size + ( $RANDOM % 8192) ))
 
 		cinfail=$(mktemp)
 		make_file "$cinfail" "client" $size