decompression:
-seperate the IPCOMP specific rule that compression must not grow the
data from general compression semantics: Introduce a special name
CRYPTO_DEFLATE_COMP_NOGROW/comp_algo_deflate_nogrow to describe
the IPCOMP semantics and use it there. (being here, fix the check
so that equal size is considered failure as well as required by
RFC2393)
Customers of CRYPTO_DEFLATE_COMP/comp_algo_deflate now always get
deflated data back, even if they are not smaller than the original.
-allow to pass a "size hint" to the DEFLATE decompression function
which is used for the initial buffer allocation. Due to the changes
done there, additional allocations and extra copies are avoided if the
initial allocation is sufficient. Set the size hint to MCLBYTES (=2k)
in IPCOMP which should be good for many use cases.
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