dropbear: Do not build static binary

Dropbear 2018.76 now uses the --enable-static option to indicate that a static
binary should be built. This will incorrectly pick up the generic buildroot
option intended for building static libraries, causing an unwanted static
binary build with BR2_SHARED_STATIC_LIBS.

Fix by appending an --disable-static configure flag, overriding the buildroot
default.

Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Reviewed-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/dropbear/dropbear.mk

@@ -27,8 +27,11 @@ DROPBEAR_MAKE = \
 	$(MAKE) MULTI=1 SCPPROGRESS=1 \
 	PROGRAMS="$(DROPBEAR_PROGRAMS)"
 
-ifeq ($(BR2_STATIC_LIBS),y)
-DROPBEAR_CONF_OPTS += --enable-static
+# With BR2_SHARED_STATIC_LIBS=y the generic infrastructure adds a
+# --enable-static flags causing dropbear to be built as a static
+# binary. Adding a --disable-static reverts this
+ifeq ($(BR2_SHARED_STATIC_LIBS),y)
+DROPBEAR_CONF_OPTS += --disable-static
 endif
 
 # Ensure that dropbear doesn't use crypt() when it's not available