tcp: restore fastopen with no data in SYN packet
tcp: restore fastopen with no data in SYN packet

Yuchung tracked a regression caused by commit 57be5bdad759 ("ip: convert
tcp_sendmsg() to iov_iter primitives") for TCP Fast Open.

Some Fast Open users do not actually add any data in the SYN packet.

Fixes: 57be5bdad759 ("ip: convert tcp_sendmsg() to iov_iter primitives")
Reported-by: Yuchung Cheng <5b5a0a360fa35167ac197fe6359c229fde284cf2@google.com>
Signed-off-by: Eric Dumazet <312c7d941f03386814be517ffdb3e0eb6624e275@google.com>
Cc: Al Viro <de609eb4d5d70b1d38ec6642adbfc33a2781f63c@zeniv.linux.org.uk>
Acked-by: Yuchung Cheng <5b5a0a360fa35167ac197fe6359c229fde284cf2@google.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs