package/xen: security bump to version 4.11.1

package/xen: security bump to version 4.11.1

The 4.11.1 release brings a large number of fixes:

https://xenproject.org/downloads/xen-archives/xen-project-411-series/xen-4111.html

Including a number of security fixes:

XSA-268: Use of v2 grant tables may cause crash on ARM (CVE-2018-15469)
XSA-269: x86: Incorrect MSR_DEBUGCTL handling lets guests enable BTS
	 (CVE-2018-15468)
XSA-272: oxenstored does not apply quota-maxentity (CVE-2018-15470)
XSA-273: L1 Terminal Fault speculative side channel (CVE-2018-3620,
         CVE-2018-3646)
XSA-275: insufficient TLB flushing / improper large page mappings with AMD
         IOMMUs
XSA-276: resource accounting issues in x86 IOREQ server handling
XSA-277: x86: incorrect error handling for guest p2m page removals
XSA-278: x86: Nested VT-x usable even when disabled (CVE-2018-18883)
XSA-279: x86: DoS from attempting to use INVPCID with a non-canonical
         addresses
XSA-280: Fix for XSA-240 conflicts with shadow paging
XSA-282: guest use of HLE constructs may lock up host

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>