fix bug in multi_asic_namespace_validation_callback

[wenyiz2021]

multi_asic.is_multi_asic is bug that returns True if function NOT exists, so the if condition will never enter, letting multi_asic_namespace_validation_callback to never work.

when changing to multi_asic.is_multi_asic(), for single-asic, we still need to ensure NO value passed inside this function. e,g, show run bgp -n asic0 on a single-asic is passing value asic0 to this function, and we want to avoid that.

What I did

How I did it

How to verify it

Before:

    # admin@str2-7050cx3-acs-02:/usr$ show ip bgp neighbor -n asic0
    # -n/--namespace is not available for single asic
    # Aborted!
    # admin@str2-7050cx3-acs-02:/usr$ show ip bgp neighbor
    # -n/--namespace is not available for single asic
    # Aborted!

After:

admin@str2-7050cx3-acs-02:/usr$ show run bgp -n asic0
-n/--namespace is not available for single asic
Aborted!
admin@str2-7050cx3-acs-02:/usr$ 
admin@str2-7050cx3-acs-02:/usr$ 
admin@str2-7050cx3-acs-02:/usr$ 
admin@str2-7050cx3-acs-02:/usr$ show run bgp -n
Error: -n option requires an argument
admin@str2-7050cx3-acs-02:/usr$ 
admin@str2-7050cx3-acs-02:/usr$ 
admin@str2-7050cx3-acs-02:/usr$ show run bgp
Building configuration...

Current configuration:
!
frr version 8.2.2
frr defaults traditional
...

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)