Revert "net: do not allow changing SO_REUSEADDR/SO_REUSEPORT on bound sockets"

Revert the patch mentioned in the subject because it breaks at least
the Avahi mDNS daemon. That patch namely causes the Ubuntu 18.04 Avahi
daemon to fail to start:

Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: Successfully called chroot().
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: Successfully dropped remaining capabilities.
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: No service file found in /etc/avahi/services.
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: SO_REUSEADDR failed: Structure needs cleaning
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: SO_REUSEADDR failed: Structure needs cleaning
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: Failed to create server: No suitable network protocol available
Jun 12 09:49:24 ubuntu-vm avahi-daemon[529]: avahi-daemon 0.7 exiting.
Jun 12 09:49:24 ubuntu-vm systemd[1]: avahi-daemon.service: Main process exited, code=exited, status=255/n/a
Jun 12 09:49:24 ubuntu-vm systemd[1]: avahi-daemon.service: Failed with result 'exit-code'.
Jun 12 09:49:24 ubuntu-vm systemd[1]: Failed to start Avahi mDNS/DNS-SD Stack.

Fixes: f396922d ("net: do not allow changing SO_REUSEADDR/SO_REUSEPORT on bound sockets")
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -728,22 +728,9 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 			sock_valbool_flag(sk, SOCK_DBG, valbool);
 		break;
 	case SO_REUSEADDR:
-		val = (valbool ? SK_CAN_REUSE : SK_NO_REUSE);
-		if ((sk->sk_family == PF_INET || sk->sk_family == PF_INET6) &&
-		    inet_sk(sk)->inet_num &&
-		    (sk->sk_reuse != val)) {
-			ret = (sk->sk_state == TCP_ESTABLISHED) ? -EISCONN : -EUCLEAN;
-			break;
-		}
-		sk->sk_reuse = val;
+		sk->sk_reuse = (valbool ? SK_CAN_REUSE : SK_NO_REUSE);
 		break;
 	case SO_REUSEPORT:
-		if ((sk->sk_family == PF_INET || sk->sk_family == PF_INET6) &&
-		    inet_sk(sk)->inet_num &&
-		    (sk->sk_reuseport != valbool)) {
-			ret = (sk->sk_state == TCP_ESTABLISHED) ? -EISCONN : -EUCLEAN;
-			break;
-		}
 		sk->sk_reuseport = valbool;
 		break;
 	case SO_TYPE: