BpfNetMaps: do not register BpfNetMaps JNI before T

BpfNetMaps needs to go through netd before T and must *never* use the
JNI methods. BpfNetMaps already throws if this code path is called
before T.

Test: TH
Change-Id: I5f69c3673cfe86ef02f9b8e35a1db63f39c3da7e
1 file changed