MDEV-33582 (3541bd63) changed the "Could not write packet"
error message in net_serv.cc to use the function
sql_print_warning(), instead of my_printf_error(). The flags
argument was not removed in this change though, so the old
flags were printed in place of the file descriptor, and all
other args are presenting for the wrong field (and length is
never showed).

This patch removes flags as a parameter to sql_print_warning().