dhcpv4: clarify variable names in dhcpv4_handle_msg()

dhcpv4: clarify variable names in dhcpv4_handle_msg()

Make it clearer which variables relate to the request, and which ones relate to
the reply that we're constructing.

Also fix the missing endianness conversion for req_leasetime (not so severe
though, a bogus leasetime value will be overridden with limits that are set
per-lease or per-interface).

Signed-off-by: David Härdeman <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/278
Signed-off-by: Álvaro Fernández Rojas <[email protected]>