NetBpfLoad: Update build constraints & comments.

Corrected the comment in Android.bp regarding the target SDK version. In NetBpfLoad.cpp, added specific handling for RiscV builds to account for its undefined minimum API level. Added an error to ensure NetBpfLoad is always compiled within an APEX. Clarified that `minSupportedKernelVer` must be 0 for APEX builds to enable runtime kernel version enforcement.

Bug: 438908493
Test: TreeHugger
Flag: EXEMPT mainline
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ie3affbfd702ff1f6d5f2887b6f56ade0ed7fb5dd
2 files changed