Fix a field in the GMLAN RDBPKTI packet

[polybassa]

Just a small fix to make this packet more correct

[codecov-io]

Codecov Report

Merging #1776 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1776      +/-   ##
==========================================
- Coverage   85.58%   85.55%   -0.03%     
==========================================
  Files         181      181              
  Lines       42209    42209              
==========================================
- Hits        36126    36114      -12     
- Misses       6083     6095      +12

Impacted Files	Coverage Δ
scapy/arch/bpf/core.py	82.1% <0%> (-1.06%)	⬇️
scapy/layers/l2.py	83.66% <0%> (-0.76%)	⬇️
scapy/automaton.py	81.84% <0%> (-0.56%)	⬇️
scapy/layers/inet6.py	88.08% <0%> (-0.24%)	⬇️
scapy/sendrecv.py	82.78% <0%> (-0.18%)	⬇️
scapy/layers/ntp.py	91.77% <0%> (+0.26%)	⬆️