bnxt_en: Fix uninitialized variable usage in bnxt_rx_pkt().

In bnxt_rx_pkt(), if the driver encounters BD errors, it will recycle
the buffers and jump to the end where the uninitailized variable "len"
is referenced.  Fix it by adding a new jump label that will skip
the length update.  This is the most correct fix since the length
may not be valid when we get this type of error.

Fixes: 6a8788f2 ("bnxt_en: add support for software dynamic interrupt moderation")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>