manifest: android-8.0.0_r30 -> android-8.1.0_r1 & lineage-15.0 -> lineage-15.1

Also switch to AOSP's versions of the following repos
 - external/libnetfilter_conntrack
 - external/libnfnetlink
 - system/hardware/interfaces
 - system/netd

Change-Id: I46fb1ef95cef62cc7f5f1600c3e578660f034e12
diff --git a/README.mkdn b/README.mkdn
index ce976c9..9470319 100644
--- a/README.mkdn
+++ b/README.mkdn
@@ -12,7 +12,7 @@
     (Go to repo you are patching, make your changes and commit)
     lineagegerrit <for(new)/changes(patch set)> <branch/change-id>
 
-    repo start lineage-15.0 .
+    repo start lineage-15.1 .
     (Make your changes and commit)
     repo upload .
 
@@ -33,7 +33,7 @@
 
 To initialize your local repository using the LineageOS trees, use a command like this:
 
-    repo init -u git://github.com/LineageOS/android.git -b lineage-15.0
+    repo init -u git://github.com/LineageOS/android.git -b staging/lineage-15.1
 
 Then to sync up: