net: ks8851: Remove type_frame_head

The packet status and length information should be extracted from the
FIFO per-packet. Adjust the code such that it reads the packet meta
data and then the packet afterward, if applicable.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eugen Hristev <eugen.hristev@microchip.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>