hw & signal: consider initial SLAB blocks

By now Signal_session_component has allocated initial SLAB
blocks in constructor, wich crashed with the root
components assumptions about the RAM quota needs of
session creation. Thus, if the background allocator was already
exhausted from component allocation the session was created
with broken initial SLAB blocks.

fix #574
issue345.diff
Fixup for previous commit

Adaptation to affinity-related interface changes.