selftests: mptcp: add infinite map testcase

Add the single subflow test case for MP_FAIL, to test the infinite
mapping case. Use the test_linkfail value to make 128KB test files.

Add a new function reset_with_fail(), in it use 'iptables' and 'tc
action pedit' rules to produce the bit flips to trigger the checksum
failures. Set validate_checksum to enable checksums for the MP_FAIL
tests without passing the '-C' argument. Set check_invert flag to
enable the invert bytes check for the output data in check_transfer().
Instead of the file mismatch error, this test prints out the inverted
bytes.

Add a new function pedit_action_pkts() to get the numbers of the packets
edited by the tc pedit actions. Print this numbers to the output.

Also add the needed kernel configures in the selftests config file.

Suggested-by: Davide Caratti <dcaratti@redhat.com>
Co-developed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>