The service-only getepinfo(2) PM call returns information about a
given endpoint. This patch extends that call so that it returns
enough information to allow correctly filling a sockcred structure.
A new getsockcred(3) function is added to libsys to fill an actual
sockcred structure with the obtained information. However, for the
caller's convenience, the groups list is kept separate.
Change-Id: I9f1a6d1a221c77eabaa3498ff4ec9a5fb922e4fd
bfa518c7ec