libdpkg: Change default lzma compression level from 9 to 6

Set the default compression level low enough to produce packages
that require no more than 10 MiB of memory to decompress, by
lowering it to 6 from 9 (this matches xz internal default compression
level).

Based-on-patch-by: Jonathan Nieder <jrnieder@gmail.com>

debian/changelog

@@ -113,6 +113,8 @@ dpkg (1.15.6) UNRELEASED; urgency=low
     instead of insecure tempnam() or tmpnam() functions.
   * Remove --license and --licence options from tools.
   * Securely remove newly installed files when rolling-back a failed unpack.
+  * Change default lzma compression level from 9 to 6.
+    Thanks to Jonathan Nieder for the initial patch.
 
   [ Modestas Vainius ]
   * Implement symbol patterns (Closes: #563752). From now on, it is possible to

lib/dpkg/compress.c

@@ -343,7 +343,7 @@ compress_lzma(int fd_in, int fd_out, int compress_level, const char *desc)
 struct compressor compressor_lzma = {
 	.name = "lzma",
 	.extension = ".lzma",
-	.default_level = 9,
+	.default_level = 6,
 	.compress = compress_lzma,
 	.decompress = decompress_lzma,
 };