ebpf: allow bpf_ktime_get_ns_proto also for networking

As this is already exported from tracing side via commit d9847d310a
("tracing: Allow BPF programs to call bpf_ktime_get_ns()"), we might
as well want to move it to the core, so also networking users can make
use of it, e.g. to measure diffs for certain flows from ingress/egress.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/trace/bpf_trace.c

@@ -79,18 +79,6 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
-static u64 bpf_ktime_get_ns(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
-{
-	/* NMI safe access to clock monotonic */
-	return ktime_get_mono_fast_ns();
-}
-
-static const struct bpf_func_proto bpf_ktime_get_ns_proto = {
-	.func		= bpf_ktime_get_ns,
-	.gpl_only	= true,
-	.ret_type	= RET_INTEGER,
-};
-
 /*
  * limited trace_printk()
  * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed