pf: Cope with overly large net.pf.states_hashsize

pf: Cope with overly large net.pf.states_hashsize

If the user configures a states_hashsize or source_nodes_hashsize value we may
not have enough memory to allocate this. This used to lock up pf, because these
allocations used M_WAITOK.

Cope with this by attempting the allocation with M_NOWAIT and falling back to
the default sizes (with M_WAITOK) if these fail.

PR:		209475
Submitted by:	Fehmi Noyan Isi <fnoyanisi AT yahoo.com>
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D14367