Ensure that java.lang.reflect.Field is initialized

Recent change in libcore (a move of clinit code
to register function for java.net.InetAddress
class) was triggering a failure in 119-noimage-patchoat
test. Failure was occurring when the test was running
without the image. This was caused by the
java.lang.reflect.Field not being initialized when
running InetAddress.<clinit>, which is a side effect
of calling JNIEnv->GetMethodId inside the libcore JNI_OnLoad.

This changes makes sure that this class is initialized
when we're running without image.

Bug: 28153851
Change-Id: I8aeb5eb312a163c452c40b851112544a8340e488