ANDROID: bpf: validate bpf_func when BPF_JIT is enabled with CFI

With CONFIG_BPF_JIT, the kernel makes indirect calls to dynamically
generated code, which the compile-time Control-Flow Integrity (CFI)
checking cannot validate. This change adds basic sanity checking to
ensure we are jumping to a valid location, which narrows down the
attack surface on the stored pointer.

In addition, this change adds a weak arch_bpf_jit_check_func function,
which architectures that implement BPF JIT can override to perform
additional validation, such as verifying that the pointer points to
the correct memory region.

Bug: 145210207
Change-Id: I1a90c70cdcef25673a870d3c4f2586a829c0d32e
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>