Apply changes to match fix of lldpd/lldpd@a9aeabd

More information about issue:
- https://nvd.nist.gov/vuln/detail/CVE-2023-41910

Suggested-by: Vincent Bernat (vincent@bernat.ch)
Signed-off-by: Georg Gebauer <georg.gebauer@zeiss.com>

By sending short SONMP packets, an attacker can make the decoder crash
by reading too much data on the heap. SONMP packets are fixed in size,
just ensure we get the enough bytes to contain a SONMP packet.

References:
* lldpd/lldpd@73d4268
* https://nvd.nist.gov/vuln/detail/CVE-2021-43612

Suggested-by: Vincent Bernat (vincent@bernat.ch)
CVE: CVE-2021-43612

Signed-off-by: Georg Gebauer <georg.gebauer@zeiss.com>