domain.te: allow /proc/net/psched access

external/sepolicy commit 99940d1a
(https://android-review.googlesource.com/123331) removed /proc/net
access from domain.te.

Around the same time, system/core commit
9a20e67fa62c1e0e0080910deec4be82ebecc922
(https://android-review.googlesource.com/123531) was checked in.
This change added libnl as a dependency of libsysutils.

external/libnl/lib/utils.c has a function called get_psched_settings(),
which is annotated with __attribute__((constructor)). This code
gets executed when the library is loaded, regardless of whether or
not other libnl code is executed.

By adding the libnl dependency, even code which doesn't use the
network (such as vold and logd) ends up accessing /proc/net/psched.

For now, allow this behavior. However, in the future, it would be
better to break this dependency so the additional code isn't loaded
into processes which don't need it.

Addresses the following denials:

  avc: denied { read } for  pid=148 comm="logd" name="psched" dev="proc" ino=4026536508 scontext=u:r:logd:s0 tcontext=u:object_r:proc_net:s0 tclass=file permissive=0
  avc: denied { read } for pid=152 comm="vold" name="psched" dev="proc" ino=4026536508 scontext=u:r:vold:s0 tcontext=u:object_r:proc_net:s0 tclass=file permissive=0
  avc: denied { read } for pid=930 comm="wpa_supplicant" name="psched" dev="proc" ino=4026536508 scontext=u:r:wpa:s0 tcontext=u:object_r:proc_net:s0 tclass=file permissive=0

Bug: 19079006
Change-Id: I1b6d2c144534d3f70f0028ef54b470a75bace1cf