On machines with strict alignment copy pfsync_state_key from packet
on stack to avoid unaligned access.

PR:		187381
Submitted by:	Lytochkin Boris <lytboris gmail.com>
Support EAGAIN in fetch_writev

Reviewed by:	des
Approved by:	des
Implement Short/Small String Optimization in SBUF(9) and change lengths and
positions in the API from ssize_t and int to size_t.

CR:		D388
Approved by:	des, bapt