chore: update Dockerfile

Dockerfile

@@ -13,8 +13,13 @@ WORKDIR /knockd
 RUN cargo build --release --target=x86_64-unknown-linux-musl
 
 FROM alpine
+
+# Install iptables
 RUN apk add --no-cache iptables
 
+# Create a symbolic link from /sbin/iptables to /usr/sbin/iptables
+RUN ln -s /sbin/iptables /usr/sbin/iptables
+
 # Copy the binary from the builder stage
 COPY --from=builder /knockd/target/x86_64-unknown-linux-musl/release/knockd /