Merge branch 'Two fixes for test_sockmap'

Zijian Zhang says:

====================
Function msg_verify_data should have context of bytes_cnt and k instead of
assuming they are zero. Otherwise, test_sockmap with data integrity test
will report some errors. I also fix the logic related to size and index j

1/ 6  sockmap::txmsg test passthrough:FAIL
2/ 6  sockmap::txmsg test redirect:FAIL
7/12  sockmap::txmsg test apply:FAIL
10/11  sockmap::txmsg test push_data:FAIL
11/17  sockmap::txmsg test pull-data:FAIL
12/ 9  sockmap::txmsg test pop-data:FAIL
13/ 1  sockmap::txmsg test push/pop data:FAIL
...
Pass: 24 Fail: 52

After fixing msg_verify_data, some of the errors are solved, but for push
pull and pop, we may need more fixes to msg_verify_data, added a TODO

10/11  sockmap::txmsg test push_data:FAIL
11/17  sockmap::txmsg test pull-data:FAIL
12/ 9  sockmap::txmsg test pop-data:FAIL
...
Pass: 37 Fail: 15

Besides, added a custom errno EDATAINTEGRITY for msg_verify_data, we
shall not ignore the error in txmsg_cork case, and fixed the txmsg_redir
in test_txmsg_pull "Test pull + redirect" case.
====================

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>