quagga: fix static link with zlib

quagga: fix static link with zlib

quagga links with zlib indirectly via netsnmp -> openssl -> zlib. quagga and
zlib both define the identically named but otherwise unrelated 'zcalloc'
symbol. This breaks static linking. Add a patch that renames the offending
symbol, thus fixing the build.

Fixes:
http://autobuild.buildroot.net/results/013/01317aeaff7d127a05e0488a51e81f2d43750687/
http://autobuild.buildroot.net/results/e9f/e9f17bb6e048c3dd3c65fc588dc5244fbbbba6fb/
http://autobuild.buildroot.net/results/72b/72b5e8a3d4c1d27c61cdad5a90691117d0dcfbb9/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>