package/libcurl: fix build with libssh2 and disabled proxy

package/libcurl: fix build with libssh2 and disabled proxy

Add patch fixing build of libssh2 support when
BR2_PACKAGE_LIBCURL_PROXY_SUPPORT is disabled.

Fixes:
http://autobuild.buildroot.net/results/113407c1721b601cf2b721d0b78392622000cc3f/
http://autobuild.buildroot.net/results/a5abdcc6a12d2326da0fe3daf9ecbb96e5c6cac3/
http://autobuild.buildroot.net/results/ab1f7b9837ac74fad359e6c239f45ed25ad31df3/

Cc: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>