Execute Sybase tests last

Better schedule as they execute faster.
Add capacity to packet to avoid having to reallocate to increase length

MARS try to use packet functions to read packets even with mars disabled

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Use packet functions to read packets even with MARS disabled

Make code more similar between MARS enabled and not.
As now we use a packet structure to store a packet use TDSPACKET->capacity
instead of TDSSOCKET->in_buf_max.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Small optimizations

Use coverage to put some compiler hints.
Replace check with an assert as condition should never happen.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
Do not reallocate packet every time

Packet was reallocated every time length changed.
Now use block size as allocation hint and use packet len to store packet
length.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>