netbpfload: Support <4.14 kernels

Change-Id: I3d6573c102c1d64a64209bf61ecb8ed0c4ecb64c

netbpfload/NetBpfLoad.cpp

@@ -225,12 +225,14 @@ int main(int argc, char** argv, char * const envp[]) {
         //  kernel does not have CONFIG_BPF_JIT=y)
         // BPF_JIT is required by R VINTF (which means 4.14/4.19/5.4 kernels),
         // but 4.14/4.19 were released with P & Q, and only 5.4 is new in R+.
-        if (writeProcSysFile("/proc/sys/net/core/bpf_jit_enable", "1\n")) return 1;
+        if (writeProcSysFile("/proc/sys/net/core/bpf_jit_enable", "1\n") &&
+            android::bpf::isAtLeastKernelVersion(4, 14, 0)) return 1;
 
         // Enable JIT kallsyms export for privileged users only
         // (Note: this (open) will fail with ENOENT 'No such file or directory' if
         //  kernel does not have CONFIG_HAVE_EBPF_JIT=y)
-        if (writeProcSysFile("/proc/sys/net/core/bpf_jit_kallsyms", "1\n")) return 1;
+        if (writeProcSysFile("/proc/sys/net/core/bpf_jit_kallsyms", "1\n") &&
+            android::bpf::isAtLeastKernelVersion(4, 14, 0)) return 1;
     }
 
     // Create all the pin subdirectories