tcp: fix synack elog crash
tcp: fix synack elog crash

The elog track, if enabled, must be initalized before synack is sent.

Type: fix

Signed-off-by: Ivan Shvedunov <5ce0144c68fb318882064dd935e03a1fcc537ac0@gmail.com>
Signed-off-by: Florin Coras <c9715e5cdf0718c2e9b10678757dfb027875eba2@cisco.com>
Change-Id: I0c585f466c9a5cbc13af971ae4951b93f9913c5f

chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp