package/mini-snmpd: bump to version 1.6

package/mini-snmpd: bump to version 1.6

Drop both patches:

 - 0001-Prepend-zero-byte-before-unsigned-integers.patch is upstream
   as of 949ae648bf7c654b8fae607a0988bfa672607156

 - 0002-mib.c-allow-unsigned-integers-to-have-an-extra-byte.patch is
   upstream as of

Use the systemd unit file provided by the upstream project instead of
our own, just add an /etc/default/ file to add the -a option to
preserve the same behavior.

This new version now needs pkg-config.

v1.6 changelog:

Bug fix release.

- Fix #16: regression in ifTable for point-to-point interfaces
- Fix #17: major memory leak in Linux backend
- Fix #18: consistent timeout handling in .conf file and command line

v1.5 changelog:

Major feature release.  Support for TCP-MIB, UDP-MIB, IP-MIB,
ifXTable with 64-bit counters.

- Majority of new features from [NDM Systems][]
- CVE fixes from [Cisco Talos Intelligence Group][talos]

- Add support for ifXTable (64-bit counters), from NDM Systems
- Add support for TCP-MIB, from NDM Systems
- Add support for UDP-MIB, from NDM Systems
- Add support for IP-MIB, from NDM Systems
- Add support for ifType
- Add support for ifMtu
- Binary and man page renamed: `mini_snmpd` --> `mini-snmpd`
- New command line option `-l LEVEL` replaces `--verbose`
- New command line option `-v` to show program version
- Create PID file when daemon is ready to receive signals
- Add support for systemd unit file on Linux
- Add support for /etc/mini-snmpd.conf, disabled by default

- CVE-2020-6060: Fix stack overflow in client connection handler
- CVE-2020-6059: Fix out-of-bounds read in parsing of SNMP packet
- CVE-2020-6058: Fix out-of-bounds read in parsing of SNMP packet
- Let `-s` flag control use of syslog, when running in foreground
- Removed all (known) GNU:isms; i.e., `__progname` and `%m`

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>