Fix: Filter bytecode alloc buffer size must be a power of 2

The current allocation policy for the filter bytecode buffer is to
double the size each time the underlying buffer can no longer contain
the entire bytecode plus padding.

In some cases, the initial allocation length is not a multiple of 2,
thus possibly leading to odd-looking allocation size each time the
buffer size is doubled.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>