build: use libcap package for Alpine images (#2644)

Author: itzg

build/alpine/install-packages.sh

@@ -27,7 +27,7 @@ apk add --no-cache -U \
     nfs-utils \
     libpcap \
     libwebp \
-    libcap-utils
+    libcap
 
 # Patched knockd
 curl -fsSL -o /tmp/knock.tar.gz https://github.com/Metalcape/knock/releases/download/0.8.1/knock-0.8.1-alpine-amd64.tar.gz