libssh2: add missing PKG_CONFIG_DEPENDS

Recently added symbols CONFIG_LIBSSH2_MBEDTLS and CONFIG_LIBSSH2_OPENSSL
require a rerun of ./configure when their selection changes. So add them
to PKG_CONFIG_DEPENDS accordingly.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

libs/libssh2/Makefile

@@ -22,6 +22,10 @@ PKG_INSTALL:=1
 PKG_LICENSE:=BSD
 PKG_LICENSE_FILES:=COPYING
 
+PKG_CONFIG_DEPENDS:= \
+	CONFIG_LIBSSH2_MBEDTLS \
+	CONFIG_LIBSSH2_OPENSSL
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/libssh2