The following has been vetted with davem w.r.t. the change to
KM_SKB_DATA. Apologies for the bug...

include/asm-*/kmap_types.h:
   Replace the unused km_type slot KM_SKB_DATA with
   KM_SKB_SUNRPC_DATA.

net/sunrpc/xdr.c:
   Replace the use of KM_USER0 with KM_SKB_SUNRPC_DATA for copying
   data from an skb into the page cache when in the sk->data_ready()
   callback.