[PATCH] tcp provider: use __ip_queue_xmit() as it is non-static on 5.4

On older kernels - 5.4 to be precise - ip_queue_xmit() is a static
function, so it is better to instrument __ip_queue_xmit() as it
is extern so not prone to optimization on 5.4 and later kernels.
With this change, the following previously-failing-on-UEK6U3 tcp tests
pass (and continue to pass when tested on an upstream kernel):

tst.ipv4localtcp.sh
tst.ipv4remotetcp.sh
tst.ipv6localtcp.sh

More work is required to fix up the tcpstate tests for UEK6U3.

Reported-by: Eugene Loh <[email protected]>
Signed-off-by: Alan Maguire <[email protected]>
---
 libdtrace/dt_prov_tcp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libdtrace/dt_prov_tcp.c b/libdtrace/dt_prov_tcp.c
index ebdcfbc9..a191efe1 100644
--- a/libdtrace/dt_prov_tcp.c
+++ b/libdtrace/dt_prov_tcp.c
@@ -37,7 +37,10 @@ static probe_dep_t	probes[] = {
 	{ "connect-refused",
 	  DTRACE_PROBESPEC_NAME,	"fbt::tcp_reset:entry" },
 	{ "connect-request",
-	  DTRACE_PROBESPEC_NAME,	"fbt::ip_queue_xmit:entry" },
+	/* ip_queue_xmit() is static for older kernels so use __ip_queue_xmit()
+	 * which is non-static for older and newer kernels.
+	 */
+	  DTRACE_PROBESPEC_NAME,	"fbt::__ip_queue_xmit:entry" },
 	/* ip6_xmit has > 6 args so cannot fentry on aarch64; use rawfbt */
 	{ "connect-request",
 	  DTRACE_PROBESPEC_NAME,	"rawfbt::ip6_xmit:entry" },
@@ -48,7 +51,7 @@ static probe_dep_t	probes[] = {
 	{ "receive",
 	  DTRACE_PROBESPEC_NAME,	"fbt::tcp_v4_send_reset:entry" },
 	{ "send",
-	  DTRACE_PROBESPEC_NAME,	"fbt::ip_queue_xmit:entry" },
+	  DTRACE_PROBESPEC_NAME,	"fbt::__ip_queue_xmit:entry" },
 	/* ip_send_unicast_reply has 10 args so cannot fentry; use rawfbt */
 	{ "send",
 	  DTRACE_PROBESPEC_NAME,	"rawfbt::ip_send_unicast_reply:entry" },
-- 
2.43.5