var: Use 16-bit container for type

[jlucovsky]

Issue: 6855: Match sigmatch type field in var and bit structs

Link to ticket: https://redmine.openinfosecfoundation.org/issues/6855

Describe changes:

• Increase type in flowbit, flowvar and generic var
• Ensure type, idx, and next pointers align on each struct.

Provide values to any of the below to override the defaults.

• To use an LibHTP, Suricata-Verify or Suricata-Update pull request,
  link to the pull request in the respective _BRANCH variable.
• Leave unused overrides blank or remove.

SV_REPO=
SV_BRANCH=
SU_REPO=
SU_BRANCH=
LIBHTP_REPO=
LIBHTP_BRANCH=

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.38%. Comparing base (3a7eef8) to head (2f8e456).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12076      +/-   ##
==========================================
- Coverage   83.42%   83.38%   -0.05%     
==========================================
  Files         910      910              
  Lines      257642   257642              
==========================================
- Hits       214949   214829     -120     
- Misses      42693    42813     +120     

Flag	Coverage Δ
fuzzcorpus	61.54% <ø> (-0.11%)	⬇️
livemode	19.44% <ø> (+0.02%)	⬆️
pcap	44.46% <ø> (-0.02%)	⬇️
suricata-verify	62.75% <ø> (-0.01%)	⬇️
unittests	59.37% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[suricata-qa]

Information: QA ran without warnings.

Pipeline 23231