dgram: add option for using recvmmsg

[theanarkh]

Add an option for using recvmmsg.

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[nodejs-github-bot]

Review requested:

• @nodejs/net

[codecov]

Codecov Report

❌ Patch coverage is 83.07692% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.55%. Comparing base (049664b) to head (aac2964).
⚠️ Report is 608 commits behind head on main.

Files with missing lines	Patch %	Lines
src/udp_wrap.cc	80.48%	4 Missing and 4 partials ⚠️
src/udp_wrap.h	76.92%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #59126      +/-   ##
==========================================
- Coverage   90.06%   88.55%   -1.51%     
==========================================
  Files         645      704      +59     
  Lines      189130   208142   +19012     
  Branches    37094    40027    +2933     
==========================================
+ Hits       170339   184323   +13984     
- Misses      11511    15828    +4317     
- Partials     7280     7991     +711     

Files with missing lines	Coverage Δ
lib/dgram.js	97.46% <100.00%> (+0.01%)	⬆️
lib/internal/dgram.js	100.00% <100.00%> (ø)
src/udp_wrap.h	85.71% <76.92%> (-14.29%)	⬇️
src/udp_wrap.cc	78.30% <80.48%> (+<0.01%)	⬆️

... and 329 files with indirect coverage changes

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[addaleax]

Can these fieds be initialized as part of the constructor member initializer list or inline in the member declaration?

[addaleax]

What if this multiplication overflows?

[addaleax]

What if malloc() returns 0?

[addaleax]

Can we CHECK() in this case that mmsg_buf_ is empty?

[addaleax]

^ This should track mmsg_buf_

[theanarkh]

@addaleax Thanks for your review ! I have updated the code.