Enabling TCP-FASTOPEN on an end-point which is in a state later than CLOSED or LISTEN, is a bug in the application. So it should not work. Also the TCP code does not (and needs not to) handle this.
This addresses also a bug found by syzkaller, which can be reproduced by the following script:
```
// http://syzkaller.nplab.de:10000/file?name=crashes%2f808457b108a581dd99facfcb23418f4a0136025f%2flog18
//01:02:45 executing program 0:
//r0 = socket$inet_tcp(0x2, 0x1, 0x0)
//setsockopt$inet_tcp_TCP_FUNCTION_BLK(r0, 0x6, 0x2000, &(0x7f00000001c0)={'rack\x00'}, 0x24)
//setsockopt$sock_int(r0, 0xffff, 0x10000, &(0x7f0000000040)=0x1, 0x4)
//bind(r0, &(0x7f00000002c0)=@in={0x10, 0x2, 0x2}, 0x10)
//setsockopt$inet_tcp_int(r0, 0x6, 0x22, &(0x7f0000000000)=0x1, 0x4)
//sendto(r0, 0x0, 0x0, 0x0, &(0x7f0000000140)=@in={0x10, 0x2, 0x0, @broadcast}, 0x10)
//syz_emit_ethernet(0x3a, &(0x7f0000000080)={@local, @random="9bddc73ea17a", [], {@ipv4={0x800, {{0x5, 0x4, 0x0, 0x0, 0x2c, 0x0, 0x0, 0x0, 0x6, 0x0, @local}, @tcp={{0x2, 0x2, 0x41424344, 0x41424344, 0x0, 0x0, 0x6, 0x83, 0x0, 0x0, 0x0, {[@sack_perm={0x4, 0x2}]}}}}}}})
//getsockopt$sock_accept_filter(r0, 0xffff, 0x1000, &(0x7f0000000400), &(0x7f0000000180)=0x100)
//setsockopt$inet_tcp_buf(r0, 0x6, 0x401, &(0x7f00000000c0)="487e3f1c48334a6607ae2be8624f8aacdf890138924f828973631c5fd08146f34a271af85553238365dba3e109e5a9bb45b241048c82e4762eccb175dec7b60e0d0c665339e5d6e2821c08b5af44e0dd8416c55616e619a1e0b18f34a3575ea0a935854751ff2444d3", 0x69)
--no_cleanup
0.000 `kldload -n tcp_rack tcp_bbr`
+0.000 `sysctl -w net.inet.tcp.fastopen.client_enable=0`
+0.000 `sysctl -w net.inet.tcp.fastopen.client_enable=1`
+0.000 `sysctl -w net.inet.tcp.functions_default=bbr`
+0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0.000 setsockopt(3, IPPROTO_TCP, TCP_FUNCTION_BLK, {function_set_name="rack", pcbcnt=0}, 36) = 0
+0.000 setsockopt(3, SOL_SOCKET, SO_REUSEPORT_LB, [1], 4) = 0
+0.000 bind(3, ..., ...) = 0
+0.000 setsockopt(3, IPPROTO_TCP, TCP_LOG, [1], 4) = 0
+0.000 sendto(3, ..., 0, 0, ..., ...) = 0
+0.000 > S 0:0(0) win 65535 <mss 1460,nop,wscale 6,sackOK,TS val 0 ecr 0>
+0.000 < SF 0:0(0) win 0 <sackOK,eol,eol>
+0.000 > S. 0:0(0) ack 1 win 65535 <mss 1460,sackOK,eol,eol>
+0.000 getsockopt(3, SOL_SOCKET, SO_ACCEPTFILTER, {af_name="", af_arg=""}, [256]) = -1 EINVAL (Invalid argument)
+0.000 setsockopt(3, IPPROTO_TCP, TCP_FASTOPEN, {enable=0x487e3f1c, psk=48334a6607ae2be8624f8aacdf890138}, 18) = 0
+0.000 close(3) = 0
//01:04:45 executing program 0:
//syz_emit_ethernet(0x36, &(0x7f0000000080)={@local, @random="9bddc73ea17a", [], {@ipv4={0x800, {{0x5, 0x4, 0x0, 0x0, 0x28, 0x0, 0x0, 0x0, 0x6, 0x0, @local={0xac, 0x14, 0x0}, @broadcast}, @tcp={{0x2, 0x2, 0x41424344, 0x41424344, 0x0, 0x0, 0x5, 0x1}}}}}})
// From the core:
// tp->t_flags = 0x80000e01 (TF_FASTOPEN|TF_NEEDFIN|TF_NEEDSYN|TF_SACK_PERMIT|TF_ACKNOW)
// tp->tp->t_rxtshift = 0
+0.000 < F 0:0(0) win 0
```