libxc/restore: Fix data auditing in handle_x86_pv_vcpu_blob()

libxc/restore: Fix data auditing in handle_x86_pv_vcpu_blob()

The current logic only works by chance, in that XSAVE records also tend to be
a multiple of 128.  Implement the missing logic for XSAVE.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
(cherry picked from commit 2a62c22715bf81c5695ae0511f89a940c7c6a492)
(cherry picked from commit 0e2bbcf8b4fe6f5fd23a341848f3785c213b26bb)
(cherry picked from commit 288872ad3bb320bd9f31145d9bd4e53786fa3245)