sftp-server: new package

Package OpenSSH's sftp-server program, so we can install it as
dependency of dropbear in a future patch. Once sftp-server is installed,
the scp tool from OpenSSH can be used with the SFTP protocol, without
enabling the legacy flag for the legacy SCP protocol.

The sftp-server binary is 126K in size.

After packaging this, I realized that we could also have used
the openssh-sftp-server package from poky:
https://gitea.sysmocom.de/sysmo-bts/generic-poky/src/branch/pyro/meta/recipes-connectivity/openssh
But let's use this extra package now, it uses the most recent OpenSSH
source and doesn't build the rest of OpenSSH which we don't need.

Related: SYS#6403
Change-Id: I376bc31413935f7a560afd916a623228550dc6fe

recipes-extra/sftp-server/sftp-server_9.3p1.bb

@@ -0,0 +1,30 @@
+# Package OpenSSH's sftp server, so the openssh client finds it and doesn't
+# need to be run with a flag to use the legacy SCP protocol (SYS#6403)
+SUMMARY = "OpenSSH's sftp-server"
+DESCRIPTION = "OpenSSH's sftp-server, to be used with dropbear"
+HOMEPAGE = "http://www.openssh.com/"
+SECTION = "console/network"
+LICENSE = "BSD"
+LIC_FILES_CHKSUM = "file://LICENCE;md5=072979064e691d342002f43cd89c0394"
+DEPENDS = ""
+SRC_URI = "https://ftp.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-${PV}.tar.gz"
+
+SRC_URI[md5sum] = "3430d5e6e71419e28f440a42563cb553"
+SRC_URI[sha256sum] = "e9baba7701a76a51f3d85a62c383a3c9dcd97fa900b859bc7db114c1868af8a8"
+
+inherit autotools
+
+EXTRA_OECONF += "--without-openssl --without-zlib"
+
+S = "${WORKDIR}/openssh-${PV}"
+
+do_compile() {
+    oe_runmake sftp-server
+}
+
+do_install() {
+    install -Dm755 "${B}"/sftp-server \
+        -t "${D}"/usr/libexec/
+}
+
+FILES_${PN} = "/usr/libexec/sftp-server"