Update javadoc of TelephonyManager#isModemEnabledForSlot

The API has always been accessible for calling app with carrier
privilege in implementation. This should be specified explicitly
in javadoc to clarify the behavior.

The @RequrePermission annotation is also updated to include
both permissions to match the fact.

Bug: 201331955
Test: m offline-sdk-docs
Change-Id: I231a0907895846bef8a97856c77587ad68a98fb0