generally prefer references in range-based for loops

[Walt Karas]

This line of code:
https://github.com/apache/trafficserver/blob/master/iocore/net/SSLSNIConfig.cc#L59

should be:
for (const auto &item : Y_sni.items) {

This causes item to be of type const Item & instead of Item.  Thus
avoiding making a copy of each element in the vector.  Look at this
example code:

https://godbolt.org/z/7j0LFT

Note in the assembler code how foo() calls the copy constructor for
Item in the for loop, and foo2() does not.