smb/client: introduce KUnit test to check search result of smb2_error_map_table

smb/client: introduce KUnit test to check search result of smb2_error_map_table

The KUnit test are executed when cifs.ko is loaded.

Just like `fs/ext4/mballoc.c` includes `fs/ext4/mballoc-test.c`.
`smb2maperror.c` also includes `smb2maperror_test.c`, allowing KUnit
tests to access any functions and variables in `smb2maperror.c`.

The maperror_test_check_search() checks whether all elements can be
correctly found in the array.

Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>