c546f36aa8https://www.illumos.org/issues/6220
5408 introduced a memleak in l2arc, namely the member b_thawed gets leaked when
an arc_hdr is realloced from full to l2only.
Reviewed by: Saso Kiselkov <saso.kiselkov@nexenta.com>
Reviewed by: Simon Klinkert <simon.klinkert@gmail.com>
Reviewed by: George Wilson <george@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Arne Jansen <sensille@gmx.net>