cxgbe: Permit multiple handlers for CPL6_FW_PLD

Currently this CPL is only used to handle replies from lookaside
crypto requests submitted by ccr(4). However, in the future this
request will be returned for other requests. Use the low bit in the
cookie field as a way to identify replies to ccr(4) vs other use
cases. This should be safe as 'struct cryptop' pointers should be
word-aligned.

Sponsored by: Chelsio Communications

(cherry picked from commit 96469647bce10132408db9b436dae8941356453b)