Unbreak VIMAGE by correctly naming the vnet pointer in struct tcp_syncache.

Reported by:	trociny, rodrigc
PR: kern/168520
Submitted by: "YAMAMOTO, Shigeru" <shigeru@iij.ad.jp>
Reviewed by: adrian

In PC-BSD 9.1, VIMAGE is enabled in the kernel config.
For laptops with Bluetooth capability, such as the HP Elitebook 8460p,
the kernel will panic upon bootup, because curthread->td_vnet
is not initialized.

Properly initialize curthread->td_vnet when initializing the Bluetooth stack.

This allows laptops such as the HP Elitebook 8460p laptop
to properly boot with VIMAGE kernels.