isisd: fix BPF ioctl() calls, treat "true" and "false" as reserved

isisd: fix BPF ioctl() calls, treat "true" and "false" as reserved

Avoid a potential conflict with the C99 defines 'true' and 'false'
found in <stdbool.h> by choosing better variable names.

Also fix the calls to these ioctls, as described in <net/bpf.h>
in FreeBSD, NetBSD, and OpenBSD:

* BIOCGBLEN, BIOCIMMEDIATE, BIOCSSEESENT (the parameter should be
of type 'u_int')

* BIOCPROMISC (there should be no parameters)