Set got_fin if in CS_SYN_RECV state and receive ST_FIN

[inetic]

Currently the server socket ignores the ST_FIN packet when in CS_SYN_RECV state. So when the other end closes the connection, the socket in CS_SYN_RECV state has no other option than to timeout.

This commit causes the serving socket not to ignore the ST_FIN packet in that state so that it can exit early.

[inetic]

Note: This commit in the clostra repository seems to serve the same purpose.

[povilasb]

Whom should we ping to get this merged? @ghazel @ssiloti :)