[mux] Mux service fails to start because of invalid service file and non-executable file

[theasianpianist]

Description

The mux.service unit file is invalid because it contains two [Service] sections. Also, the mark_dhcp_packet.py file referenced in this unit file is not executable.

Steps to reproduce the issue:

1. Load 202012.43 or .44 on a dual ToR testbed
2. systemctl status mux

Describe the results you received:

admin@str2-7050cx3-acs-06:~$ systemctl status mux
● mux.service - MUX Cable Container
     Loaded: bad-setting (Reason: Unit mux.service has a bad unit file setting.)
     Active: inactive (dead)

Describe the results you expected:

Service is running correctly

Output of show version:

(paste your output here)

Output of show techsupport:

(paste your output here or download and attach the file here )

Additional information you deem important (e.g. issue happens only occasionally):