sock: expose so_timestamp options for mptcp

This exports SO_TIMESTAMP_* function for re-use by MPTCP.

Without this there is too much copy & paste needed to support
this from mptcp setsockopt path.
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2743,6 +2743,7 @@ static inline bool sk_dev_equal_l3scope(struct sock *sk, int dif)
 void sock_def_readable(struct sock *sk);
 
 int sock_bindtoindex(struct sock *sk, int ifindex, bool lock_sk);
+void sock_set_timestamp(struct sock *sk, int optname, bool valbool);
 void sock_enable_timestamps(struct sock *sk);
 void sock_no_linger(struct sock *sk);
 void sock_set_keepalive(struct sock *sk);

net/core/sock.c

@@ -776,6 +776,24 @@ void sock_enable_timestamps(struct sock *sk)
 }
 EXPORT_SYMBOL(sock_enable_timestamps);
 
+void sock_set_timestamp(struct sock *sk, int optname, bool valbool)
+{
+	switch (optname) {
+	case SO_TIMESTAMP_OLD:
+		__sock_set_timestamps(sk, valbool, false, false);
+		break;
+	case SO_TIMESTAMP_NEW:
+		__sock_set_timestamps(sk, valbool, true, false);
+		break;
+	case SO_TIMESTAMPNS_OLD:
+		__sock_set_timestamps(sk, valbool, false, true);
+		break;
+	case SO_TIMESTAMPNS_NEW:
+		__sock_set_timestamps(sk, valbool, true, true);
+		break;
+	}
+}
+
 void sock_set_keepalive(struct sock *sk)
 {
 	lock_sock(sk);
@@ -989,16 +1007,10 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case SO_TIMESTAMP_OLD:
-		__sock_set_timestamps(sk, valbool, false, false);
-		break;
 	case SO_TIMESTAMP_NEW:
-		__sock_set_timestamps(sk, valbool, true, false);
-		break;
 	case SO_TIMESTAMPNS_OLD:
-		__sock_set_timestamps(sk, valbool, false, true);
-		break;
 	case SO_TIMESTAMPNS_NEW:
-		__sock_set_timestamps(sk, valbool, true, true);
+		sock_set_timestamp(sk, valbool, optname);
 		break;
 	case SO_TIMESTAMPING_NEW:
 	case SO_TIMESTAMPING_OLD: