Avoid SELinux violation at vndservicemanager

Avoid following SELinux violation.

avc: denied { read } for comm="vndservicemanag"
name="nonplat_service_contexts" dev="rootfs" ino=17045
scontext=u:r:vndservicemanager:s0
tcontext=u:object_r:service_contexts_file:s0 tclass=file permissive=0
ppid=1 pcomm="init" pgid=1 pgcomm="init"

This violation caused by vndservicemanager reading service_contexts at
svcmgr_handler(). In main() loading as well, processing is divided by
the VENDORSERVICEMANAGER flag. Therefore, even in svcmgr_handler(),
processing is divided by flags like main().

Bug: 62562415
Test: mma
Change-Id: I06b0308a80fc6ea1ca57cd10d9555dd269b8e12d