bpf: convert several boolean natured fields of bpf_d to flags

[glebius]

Summary

This shrinks the structure a bit. Should be no functional change.

[markj]

sys/net/bpf.c

876

No lock is held here.

1511

Most of the accesses/updates are locked by the bpfd lock, so this update is unlocked.

[glebius]

sys/net/bpf.c

1511

With this revision I don't intend to fix any bugs, just make struct smaller and make it possible to pass flags to bif_write method.

[markj]

sys/net/bpf.c

1511

Ok, but you're also introducing new bugs. Before, the code was performing unsynchronized stores to different fields. Now they are doing read-modify-writes to the same field, so setting one flag might clobber a different one. That wasn't possible before.

[glebius]

The d_promisc appears to be locked by the global BPF_LOCK(). Thus, remove it
from this changes. This addresses Mark's comments.