libssh: compile against MbedTLS instead of OpenSSL

Since 2017 libssh supports to be compiled against libmbedtls instead of
libopessl, OpenWrt ships mbedtls by default, while depending on OpenSSL
increase image size by almost 1.5MB unnecessarily.

Signed-off-by: Gioacchino Mazzurco <gio@eigenlab.org>

libs/libssh/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libssh
 PKG_VERSION:=0.10.4
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://www.libssh.org/files/0.10/
@@ -32,7 +32,7 @@ define Package/libssh
   CATEGORY:=Libraries
   URL:=$(PKG_SOURCE_URL)
   TITLE:=SSH library
-  DEPENDS:=+libpthread +librt +zlib +libopenssl
+  DEPENDS:=+libpthread +librt +zlib +libmbedtls
 endef
 
 define Package/libssh/description
@@ -46,6 +46,7 @@ CMAKE_OPTIONS += \
 	-DHAVE_TERMIOS_H=1 \
 	-DWITH_EXAMPLES:BOOL=OFF \
 	-DWITH_GCRYPT:BOOL=OFF \
+	-DWITH_MBEDTLS:BOOL=ON \
 	-DWITH_GSSAPI:BOOL=OFF \
 	-DWITH_LIBZ:BOOL=ON \
 	-DWITH_NACL:BOOL=OFF \