MFC r283291: don't use CALLOUT_MPSAFE with callout_init()

The main purpose of this MFC is to reduce conflicts for other merges.
Parts of the original change have already "trickled down" via individual MFCs.

MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

Merge r268492:
On machines with strict alignment copy pfsync_state_key from packet
on stack to avoid unaligned access.

PR: 187381

Merge r261882, r261898, r261937, r262760, r262799:
Once pf became not covered by a single mutex, many counters in it became
race prone. Some just gather statistics, but some are later used in
different calculations.

A real problem was the race provoked underflow of the states_cur counter
on a rule. Once it goes below zero, it wraps to UINT32_MAX. Later this
value is used in pf_state_expires() and any state created by this rule
is immediately expired.

Thus, make fields states_cur, states_tot and src_nodes of struct
pf_rule be counter(9)s.

MFC r263710, r273377, r273378, r273423 and r273455:

- De-vnet hash sizes and hash masks.
- Fix multiple issues related to arguments passed to SYSCTL macros.

Sponsored by: Mellanox Technologies

Merge r268492:
On machines with strict alignment copy pfsync_state_key from packet
on stack to avoid unaligned access.

PR: 187381

Merge r261882, r261898, r261937, r262760, r262799:
Once pf became not covered by a single mutex, many counters in it became
race prone. Some just gather statistics, but some are later used in
different calculations.

A real problem was the race provoked underflow of the states_cur counter
on a rule. Once it goes below zero, it wraps to UINT32_MAX. Later this
value is used in pf_state_expires() and any state created by this rule
is immediately expired.

Thus, make fields states_cur, states_tot and src_nodes of struct
pf_rule be counter(9)s.