Honor reply_header_max_size for received FTP control responses (#2417)

Honor reply_header_max_size for received FTP control responses (#2417)

2023 commit 801593a claimed that `reply_header_max_size` applied to "FTP
command responses". However, that misleading claim probably only covered
FTP command replies that were parsed while being loaded from cache[^1],
after being converted to HttpReply objects and written to Store. The
same claim now applies to all received/raw FTP command replies as well.

[^1]: Both store_client::parseHttpHeadersFromDisk() and
MemStore::copyFromShm() called HttpReply::parseTerminatedPrefix().

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