Fix Errno Sign For XfrmController

XfrmController functions and status all use
positive errno values; however in the instances
where -errno is returned, namely for calls to
sendNetlinkRequest(), the sign is incorrect,
which leads to errors not being properly processed.

Bug: 62778032
Test: TestXfrmControllerInit on AOSP/master - marlin
Change-Id: Ie5ac8f032af0021e1dc22b523dec801d9c62bf41