[COMMITTED 2.36] syslog: Fix large messages (BZ#29536)

[Adhemerval Zanella Netto]

On 30/08/22 09:06, Adhemerval Zanella wrote:
> The a583b6add407c17cd change did not handle large messages that
> would require a heap allocation correctly, where the message itself
> is not take in consideration.
> 
> This patch fixes it and extend the tst-syslog to check for large
> messages as well.
> 
> Checked on x86_64-linux-gnu.
> 
> Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
> (cherry picked from commit 52a5be0df411ef3ff45c10c7c308cb92993d15b1)

And I need to sort out my environment to avoid send this kind of messages
to libc-alpha, sorry for the noise.