MINOR: stick-table: store a per-table hash seed and use it

MINOR: stick-table: store a per-table hash seed and use it

Instead of using memcpy() to concatenate the table's name to the key when
allocating an stksess, let's compute once for all a per-table seed at boot
time and use it to calculate the key's hash. This saves two memcpy() and
the usage of a chunk, it's always nice in a fast path.

When tested under extreme conditions with a 80-byte long table name, it
showed a 1% performance increase.