install.sh: prefix cross-compile outputs with gopacket-

The native install already renamed each tool to gopacket-<toolname>
before copying to /usr/local/bin, but the portable and windows cross-
compile targets dropped raw binaries like ping.exe, net.exe, reg.exe,
attrib.exe, services.exe into ./dist/. When a user copies one of those
to a Windows host and runs it from the same directory, cmd.exe's PATH
resolution picks up the local binary before the Windows built-in of
the same name, shadowing tools users rely on. The portable target on
Linux has the same risk for binaries named ping, net, etc.

Applies the same normalization (lowercase, underscores to hyphens)
and gopacket- prefix the native install already uses, but at build
time for the cross-compile targets. Native behavior is unchanged:
./bin/ still gets raw names so install_native can prefix on copy.

install.sh

@@ -272,7 +272,20 @@ build_target() {
             continue
         fi
         echo -n "  ${tool}... "
-        local out_path="${outdir}/${tool}${exe_suffix}"
+        # Cross-compile outputs get the same gopacket- prefix as the native
+        # install, so users copying a .exe to a Windows host don't end up with
+        # ping.exe / net.exe / reg.exe shadowing built-ins of the same name.
+        # Native stays as the raw name here; install_native prefixes when it
+        # copies to INSTALL_DIR.
+        local out_name
+        if [ "$t" = "native" ]; then
+            out_name="$tool"
+        else
+            local normalized
+            normalized=$(echo "$tool" | tr '[:upper:]' '[:lower:]' | tr '_' '-')
+            out_name="gopacket-${normalized}"
+        fi
+        local out_path="${outdir}/${out_name}${exe_suffix}"
         local build_cmd=(go build -o "$out_path")
         if [ "$t" = "native" ]; then
             # Static-link libgcc so binaries run on minimally-versioned hosts.