[core] Fixed the problem of getting option values from groups

[ethouris]

Fixes #2887

Fixed: the group's getOpt returns one of the possible way:

1. A groupwise option returns the value from its own fields
2. A socketwise option is returned either from the option storage, or default values.
3. Some options can't be requested on a group and for them error should be reported.

There was also added some options that should have been returend as groupwise, but were not updated accordingly.

[ethouris]

Please ignore multiple commits. I have mistakelny taken a branch of another PR to check in the changes, only later merged to the right branch.

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (16cb043) 64.79% compared to head (2939a2b) 64.88%.

Files	Patch %	Lines
srtcore/group.cpp	35.71%	18 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2891      +/-   ##
==========================================
+ Coverage   64.79%   64.88%   +0.08%     
==========================================
  Files         101      101              
  Lines       17482    17540      +58     
==========================================
+ Hits        11328    11381      +53     
- Misses       6154     6159       +5     

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[maxsharabayko]

Would it be possible to rebase to exclude the merge commit? Otherwise I'd have to squash merge.

[ethouris]

Ok, I'll recreate the branch

[maxsharabayko]

So you squash-merged it yourself... I intended to preserve those two commits: [core] and [tests]. That was the reason for my question about excluding the merge commit. I could then rebase those two commits on the master branch.

[ethouris]

I didn't squash-merge. Both the fix and the test were submitted in a single commit.