swcr_newsession can change the pointer for swcr_sessions which races with
swcr_process which is looking up entries in this array.
Add a rwlock that protects changes to the array pointer so that
swcr_newsession and swcr_process no longer race.
Original patch by: Steve O'Hara-Smith <Steve.OHaraSmith@isilon.com>
Reviewed by: jmg
Sponsored by: EMC / Isilon Storage Division