tcp: bpf: Support bpf_getsockopt for TCP_BPF_RTO_MIN

Support bpf_getsockopt if application tries to know what the RTO MIN
of this socket is.

Signed-off-by: Jason Xing <[email protected]>
Signed-off-by: Martin KaFai Lau <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: JasonXing

net/core/filter.c

@@ -5295,6 +5295,12 @@ static int bpf_sol_tcp_getsockopt(struct sock *sk, int optname,
 		memcpy(optval, &cb_flags, optlen);
 		break;
 	}
+	case TCP_BPF_RTO_MIN: {
+		int rto_min_us = jiffies_to_usecs(inet_csk(sk)->icsk_rto_min);
+
+		memcpy(optval, &rto_min_us, optlen);
+		break;
+	}
 	default:
 		return -EINVAL;
 	}