MFC 338013: bsnmpd(8): fix and optimize interface description processing

* correctly prepare a buffer to obtain interface description from a kernel
and truncate long description instead of dropping it altogether and
spamming logs;
* skip calling strlen() for each description and each SNMP request
for MIB-II/ifXTable's ifAlias.
* teach bsnmpd to allocate memory dynamically for interface descriptions
to decrease memory usage for common case and not to break
if long description occurs;

PR: 217763
Reviewed by: harti and others
Differential Revision: https://reviews.freebsd.org/D16459

MFC r310950:

MIB-II: use strlcpy when copying interface names to .ifr_name

.ifra_name is assumed to be NUL terminated; using strlcpy(3)
ensures that it's indeed NUL terminated whereas strncpy does
not.

Tested and verified as follows with a combination of ifconfig,
snmpget, and snmpset:

% ifconfig create lo1 127.0.0.2/8
% SNMPARGS="-v 3 -n '' -u bsnmp -A bsnmptest -l authPriv -a sha -x des -X bsnmptest localhost"
% snmpget $SNMPARGS IF-MIB::ifAdminStatus.4
IF-MIB::ifAdminStatus.4 = INTEGER: up(1)
% snmpset $SNMPARGS IF-MIB::ifAdminStatus.4 i 2
IF-MIB::ifAdminStatus.4 = INTEGER: down(2)
% snmpget $SNMPARGS IF-MIB::ifAdminStatus.4
IF-MIB::ifAdminStatus.4 = INTEGER: down(2)
% snmpset $SNMPARGS IF-MIB::ifAdminStatus.4 i 1
IF-MIB::ifAdminStatus.4 = INTEGER: up(1)
% snmpget $SNMPARGS IF-MIB::ifAdminStatus.4
IF-MIB::ifAdminStatus.4 = INTEGER: up(1)

CID: 1009652-1009656, 1349850

MFstable/11 r310901:

MFC r310648:

style(9): clean up trailing whitespace

MFC r294507,r294567,r299466:

r294507 (by harti):

Fill the ifAlias leaf of the ifXTable with the interface description
if there is one available and it fits into the maximum size (64 characters).

r294567 (by bz):

Change the variable to a #define in order to make gcc happy which
otherwise will complain about "variably modified 'alias' at file scope".
Unbreaks the build on gcc platforms.

r299466 (by cem):

bsnmpd: Fix size of trapsink::comm to match other community arrays

This fixes a number of possible strcpy() buffer overruns between the various
community strings in trap.c.

CIDs: 1006820, 1006821, 1006822

MFC r298462:

Return `ret` in op_ifentry(..) to mute a -Wunused-but-set-variable warning

This will also now detect error conditions with
value->var.subs[sub - 1] == LEAF_ifPhysAddress where `string_get(..)`
could fail if iifp->physaddr and/or iifp->physaddrlen were deemed
invalid.

CID: 1006551

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Properly detect interface's state in the LINK_STATE_UNKNOWN case.

MFC after: 1 week

This commit was generated by cvs2svn to compensate for changes in r156066,
which included commits to RCS files with non-trunk default branches.

Virgin import of bsnmpd 1.12

Vendor fix: make mibII HC counters really 64-bit on 32-bit platforms by polling
the kernel periodically.

Submitted by: glebius (partly)

Vendor patch: fix the reporting of ifOperStatus. We now consider an
interface up when it is running AND the link is not down (that is, it is
up or unknown). If the interface is running but the link is down, we return
state 'dormant', because we're waiting for an external event. Otherwise
the interface is 'down'.

Submitted by: csjp
Reviewed by: glebius

Virgin import of bsnmpd 1.10

Virgin import of bsnmpd 1.8

Virgin import of bsnmpd 1.7

Import of bsnmpd 1.6

Virgin import of bsnmpd 1.5a

Virgin import of bsnmp 1.4