Move icl_pdu_get_data() and xpt_done() out of initiator's session lock.

During heavy reads data copying in icl_pdu_get_data() may consume large
percent of CPU time.  Moving it out of the lock significantly reduces
lock hold time and respectively lock congestion on read operations.

MFC after:	2 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274843 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f