Fix 502 Bad Gateway caused by print() in LuCI template

[lushangkan]

Problem

The template renders the wireless profile into a <textarea> using Lua's print():

for line in fd:lines() do
    print(line)
end

print() writes to stdout instead of the LuCI template output stream. On recent LuCI/uCode based systems, this corrupts the CGI response and causes:

502 Bad Gateway
The process did not produce any response

Reason

Older LuCI environments tolerated or redirected print() differently, but recent LuCI/uCode based systems expose this issue because print() writes to the CGI stdout instead of the template output stream.

Steps to reproduce:

1. Open Wireless Parameters (Raw Configuration)
2. The page returns:

502 Bad Gateway
The process did not produce any response

Cause:

Lua print() is used inside a LuCI template, which writes to stdout and breaks the HTTP response.

Fix

Instead of printing each line with print(), read the file into a string and render it using LuCI template output (<%= ... %>). This avoids writing directly to stdout and is compatible with both legacy and current LuCI implementations.