tcp: remove inet_rtx_syn_ack()

inet_rtx_syn_ack() is a simple wrapper around tcp_rtx_synack(),
if we move req->num_retrans update.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250626153017.2156274-3-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>