usr.sbin: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

bsnmpd/modules/snmp_lm75: Fix typos

Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/653

No need for each bsnmpd(1) module to open connection to syslog

bsnmpd(1) main does that early on init and the connection is available
to all loaded modules

Event: Vienna Hackathon 2019
PR: 233431 , 221487
MFC after: 2 weeks

Simplify the code a little bit using the update_sensor_sysctl() routine to
retrieve the sensor temperature.

This also avoid the overflow that could happen on sysctlnametomib(3)
because the code was not checking the length of the mib array.

CID: 1222504

Correct the buffer length check to avoid overflows.

Found with: Coverity Scan
CID: 1222502, 1222503

Adds the bsnmp module to export the temperature data from lm75 sensors on
the system.

Together with lm75(4) this module allows easy temperature monitoring over
SNMP, specially for embedded systems.

Manual page reviewed by: brueffer (D128)