Added the option to show network namespace names where possible

[owen5mith]

Hello,

Firstly, thanks for this great project, it's come in very handy!

This PR adds the option to show network namespace names (where possible). This is disabled by default. Two new flags have been added:

1. --output-netns-names=(true|false) - This enables including the information in the table or JSON output.
2. --netns-names-max-length - This sets the maximum amount of chars from each name to display. Only relevant when using the table output.

Example Outputs

Default + output-netns-names (pwru --output-netns-names=true)

SKB                CPU PROCESS          NETNS      MARK/x        IFACE       PROTO  MTU   LEN      NETNS NAME    TUPLE FUNC
0xffff0000cbc22700 2   ~/bin/ping:34688 4026532543 0               0         0x0000 1500  84       my-netns     10.200.1.2:0->10.200.1.1:0(icmp) ip_send_skb

No Meta (pwru --output-netns-names=true --output-meta=false)

SKB                CPU PROCESS             NETNS NAME    TUPLE FUNC
0xffff0000c0fe1b00 0   ~/bin/ping:34688    my-netns     10.200.1.2:0->10.200.1.1:0(icmp) ip_send_skb

I'm conscious there isn't an open issue for this, apologies. I completely understand if this isn't wanted functionality.

[brb]

Thanks!