bnxt_en: Return error if FW returns more data than dump length

If any change happened in the configuration of VF in VM while
collecting live dump, there could be a race and firmware can return
more data than allocated dump length. Fix it by keeping track of
the accumulated core dump length copied so far and abort the copy
with error code if the next chunk of core dump will exceed the
original dump length.

Fixes: 6c5657d0

 ("bnxt_en: Add support for ethtool get dump.")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>