dropbear: allow disabling support for scp

If not needed, disabling scp allows for a nice size reduction.

Dropbear executable size comparison:

153621 bytes (baseline)
133077 bytes (without scp)

In other words, we trim a total of 20544 bytes.

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

package/network/services/dropbear/Config.in

@@ -95,4 +95,8 @@ config DROPBEAR_DBCLIENT
 	bool "Build dropbear with dbclient"
 	default y
 
+config DROPBEAR_SCP
+	bool "Build dropbear with scp"
+	default y
+
 endmenu

package/network/services/dropbear/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=dropbear
 PKG_VERSION:=2020.80
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:= \
@@ -31,7 +31,7 @@ PKG_CONFIG_DEPENDS:= \
 	CONFIG_DROPBEAR_CURVE25519 CONFIG_DROPBEAR_ZLIB \
 	CONFIG_DROPBEAR_ED25519 CONFIG_DROPBEAR_CHACHA20POLY1305 \
 	CONFIG_DROPBEAR_UTMP CONFIG_DROPBEAR_PUTUTLINE \
-	CONFIG_DROPBEAR_DBCLIENT
+	CONFIG_DROPBEAR_DBCLIENT CONFIG_DROPBEAR_SCP
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -53,7 +53,9 @@ define Package/dropbear
   CATEGORY:=Base system
   TITLE:=Small SSH2 client/server
   DEPENDS:= +DROPBEAR_ZLIB:zlib
-  ALTERNATIVES:=100:/usr/bin/scp:/usr/sbin/dropbear
+  ALTERNATIVES:=
+  $(if $(CONFIG_DROPBEAR_SCP),ALTERNATIVES+= \
+	  100:/usr/bin/scp:/usr/sbin/dropbear,)
   $(if $(CONFIG_DROPBEAR_DBCLIENT),ALTERNATIVES+= \
 	  100:/usr/bin/ssh:/usr/sbin/dropbear,)
 
@@ -146,7 +148,7 @@ endef
 define Build/Compile
 	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) \
 		$(TARGET_CONFIGURE_OPTS) \
-		PROGRAMS="dropbear $(if $(CONFIG_DROPBEAR_DBCLIENT),dbclient,) dropbearkey scp" \
+		PROGRAMS="dropbear $(if $(CONFIG_DROPBEAR_DBCLIENT),dbclient,) dropbearkey $(if $(CONFIG_DROPBEAR_SCP),scp,)" \
 		MULTI=1 SCPPROGRESS=1
 	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) \
 		$(TARGET_CONFIGURE_OPTS) \