[openssl/openssl] 20af01: Fix documentation of BIO_FLAGS_BASE64_NO_NL

[Tomas Mraz]

  Branch: refs/heads/OpenSSL_1_1_1-stable
  Home:   https://github.openssl.org/openssl/openssl
  Commit: 20af01d46ca4086f6b1339b67c15c81d8b4a040d
      https://github.openssl.org/openssl/openssl/commit/20af01d46ca4086f6b1339b67c15c81d8b4a040d
  Author: Fraser Tweedale <ftweedal at redhat.com>
  Date:   2022-06-16 (Thu, 16 Jun 2022)

  Changed paths:
    M doc/man3/BIO_f_base64.pod

  Log Message:
  -----------
  Fix documentation of BIO_FLAGS_BASE64_NO_NL

Commit 8bfb7506d210841f2ee4eda8afe96441a0e33fa5 updated
`BIO_f_base64(3)` to improve the documentation of the
`BIO_FLAGS_BASE64_NO_NL` flag.  In particular, the updated text
states that when this flag is used, all newlines in the input are
ignored.  This is incorrect, as the following program proves:

```c

unsigned char *in_buf =
    "IlRoZSBxdWljayBicm93biBmb3gganVt\ncHMgb3ZlciBhIGxhenkgZG9nLiI=\n";

int main(int argc, char **argv) {
    BIO *b64 = BIO_new(BIO_f_base64());
    if (b64 == NULL) return 1;
    BIO_set_flags(b64, BIO_get_flags(b64) | BIO_FLAGS_BASE64_NO_NL);
    int in_len = strlen(in_buf);
    BIO *in = BIO_new_mem_buf(in_buf, in_len);
    if (in == NULL) return 2;
    in = BIO_push(b64, in);
    unsigned char *out_buf = calloc(in_len, sizeof(unsigned char));
    if (out_buf == NULL) return 3;
    size_t out_len;
    int r = BIO_read_ex(in, out_buf, in_len, &out_len);
    printf("rv = %d\n", r);
    printf("decoded = %s\n", out_buf);
    return 0;
}
```

Update the text of `BIO_f_base64(3)` to clarify that when the flag
is set, the data must be all on one line (with or without a trailing
newline character).

Signed-off-by: Fraser Tweedale <ftweedal at redhat.com>

Reviewed-by: Paul Dale <pauli at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18568)

(cherry picked from commit 0edcbacca99ab2b716da395f204610fc2775ea83)