TCP_DEFER_ACCEPT socket option is not supported

[candrews]

Is your feature request related to a problem? Please describe.
When starting apache 2 httpd with LD_PRELOAD=/usr/lib64/mptcpize/libmptcpwrap.so, this error is logged at startup:

[core:warn] [pid 2238878:tid 139880911450688] (95)Operation not supported: AH00076: Failed to enable APR_TCP_DEFER_ACCEPT

Describe the solution you'd like
mptcpize should support the TCP_DEFER_ACCEPT socket option.

Describe alternatives you've considered
I've considered ignoring the warning :)

However, there are other applications that will fail if this socket option isn't supported, such as those based on Apache Thrift. For example, MapD fails with:

TServerSocket::listen() setsockopt() TCP_DEFER_ACCEPT Protocol not available

[mjmartineau]

Hi @candrews, this is a kernel issue not a mptcpize problem. I tried to transfer this issue over to https://github.com/multipath-tcp/mptcp_net-next/issues but Github wouldn't allow the cross-organization transfer.

Would you like to resubmit this issue there to preserve your author information, or should I create a new issue referencing this one?

[candrews]

Created multipath-tcp/mptcp_net-next#271 - thank you!