net: qed: fix buffer overflow on ethtool -d

When generating debug dump, driver firstly collects all data in binary
form, and then performs per-feature formatting to human-readable if it
is supported.

For ethtool -d, this is roughly incorrect for two reasons. First of all,
drivers should always provide only original raw dumps to Ethtool without
any changes.
The second, and more critical, is that Ethtool's output buffer size is
strictly determined by ethtool_ops::get_regs_len(), and all data *must*
fit in it. The current version of driver always returns the size of raw
data, but the size of the formatted buffer exceeds it in most cases.
This leads to out-of-bound writes and memory corruption.

Address both issues by adding an option to return original, non-formatted
debug data, and using it for Ethtool case.

v2:
 - Expand commit message to make it more clear;
 - No functional changes.

Fixes: c965db44

 ("qed: Add support for debug data collection")
Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>