drbd: Fix regression in recv_bm_rle_bits (compressed bitmap)

drbd: Fix regression in recv_bm_rle_bits (compressed bitmap)

We used to be16_to_cpu the length field in our received packet header.
drbd commit 17c854fea474a5eb3cfa12e4fb019e46debbc4ec
    drbd: receiving of big packets, for payloads between 64kByte and 4GByte
changed this, but forgot to adjust a few places where we relied on
h->length being in native byte order.

This broke the receiving side of the RLE compressed bitmap exchange.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>