sepolicy: fix wigignpt access to network parameters

Add rule to fix problem with accessing sysfs network
parameters on recent android versions.
Based on this audit log:
avc: denied { search } for pid=1024 comm="wigignpt" name="net" dev="sysfs" ino=41025 scontext=u:r:wigignpt:s0 tcontext=u:object_r:sysfs_net:s0 tclass=dir permissive=0

Change-Id: I0c847447acf3ffd7903a62e0139e69308dca851f