[buildbot] buildworker: add swig package

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch master:
https://git.openwrt.org/3776a9157532e69478ef03236d22254267a4f12e

commit 3776a9157532e69478ef03236d22254267a4f12e
Author: Petr Štetiar <ynezz at true.cz>
AuthorDate: Fri Mar 12 14:57:44 2021 +0100

    buildworker: add swig package
    
    The U-Boot build for more and more SoCs is using binman by default to
    combine the images (SPL, U-Boot, ...). Binman is build from the U-Boot
    project and it needs swig to build. We have multiple patches in OpenWrt
    to remove this dependency from U-Boot, but it costs more and more time
    to revert back to the old code. We have them in sunxi and rockchip
    U-Boot, the Mediatek U-Boot build failed some time ago because of
    missing swig in build bots.
    
    In U-Boot 2021.01 the binman usage changed again, so it needs further
    adaptations.
    
    Building swig in OpenWrt tools will not be easy. We needs swig with
    Python bindings and this version needs the Python development headers to
    build.
    
    References: https://lists.infradead.org/pipermail/openwrt-devel/2021-February/033654.html
    Suggested-by: Hauke Mehrtens <hauke at hauke-m.de>
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 docker/buildworker/Dockerfile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docker/buildworker/Dockerfile b/docker/buildworker/Dockerfile
index d568ebb..8e7960b 100644
--- a/docker/buildworker/Dockerfile
+++ b/docker/buildworker/Dockerfile
@@ -24,6 +24,7 @@ RUN \
 		rsync \
 		signify-openbsd \
 		subversion \
+		swig \
 		pv \
 		pwgen \
 		python3 \