Win32: perl: Avoid transport initialization failure in Perl SNMP agents

Avoid that the followingn message is printed during startup of a Perl SNMP
agent:

netsnmp_assert s != (-1) failed ..\..\snmplib\transports\snmpUDPBaseDomain.c:484

See also commit 36a7de7230fbbbb52cc37cbbed281eb559404be9.
CHANGES: snmpd: Add a missing function declaration
Merge branch 'V5-4-patches' into V5-5-patches

* V5-4-patches:
  CHANGES: snmpd: Add a missing function declaration
Merge branch 'V5-5-patches' into V5-6-patches

* V5-5-patches:
  CHANGES: snmpd: Add a missing function declaration
CHANGES: snmpd: Remove some unused includes
Merge branch 'V5-4-patches' into V5-5-patches

* V5-4-patches:
  CHANGES: snmpd: Remove some unused includes
Merge branch 'V5-5-patches' into V5-6-patches

* V5-5-patches:
  CHANGES: snmpd: Remove some unused includes
CHANGES: snmpd: Use 0 for the ignored numvars argument to netsnmp_register_mib

The numvars argument of netsnmp_register_mib is ignored if the var
argument is NULL. In order to unify this use of it with all other ones,
change it from 1 to 0
Merge branch 'V5-4-patches' into V5-5-patches

* V5-4-patches:
  CHANGES: snmpd: Use 0 for the ignored numvars argument to netsnmp_register_mib
Merge branch 'V5-5-patches' into V5-6-patches

* V5-5-patches:
  CHANGES: snmpd: Use 0 for the ignored numvars argument to netsnmp_register_mib
snmpnetstat: fix statistics for ipv6
Merge branch 'V5-4-patches' into V5-5-patches
Merge branch 'V5-5-patches' into V5-6-patches
CHANGES: snmplib: Avoid failure to trigger sign extension due to overlong types

In asn_realloc_rbuild_signed_int64 the algorithm assumes that shifting
values greater than 0x7fffffff right is an arithmetic shift that will
shift in 1's. On hosts where long is more than 32 bits the use of long
for 'low' and 'high' makes this assumption false.

Thanks to rkj@softhome.net for reporting this issue.
Merge branch 'V5-4-patches' into V5-5-patches

* V5-4-patches:
  CHANGES: snmplib: Avoid failure to trigger sign extension due to overlong types
CHANGES: snmplib: Correct the type check for opaque variables when decoding counter64 values.

Thanks to rkj@softhome.net for reporting this issue.
Merge branch 'V5-5-patches' into V5-6-patches

* V5-5-patches:
  CHANGES: snmplib: Correct the type check for opaque variables when decoding counter64 values.
  CHANGES: snmplib: Avoid failure to trigger sign extension due to overlong types
CHANGES: testing: Add tests for asn_realloc_rbuild_*int* and tests for opaque unsigned 64-bit types.