updated server command line options with --listen

[ntalentac]

fixed now missing cli option. The -p no longer exists.

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This change is 

[FR4NK-W]

Thanks for your contribution and noticing that the scion-bwtestserver now only uses the --listen flag.
The -s flag still exists and is used by the scion-bwtestclient.

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions / 0 of 1 LGTMs obtained / 0 of 1 approvals obtained

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content/apps/bwtester.md line 24 at r1 (raw file):

scion-bwtestclient -p

scion-bwtestclient in the latest version (3.3.1) is still using the -s flag to specify the server address.

Code quote:

-p 

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content/apps/bwtester.md line 50 at r1 (raw file):

where -p specifies your server port.

please also update the comment

Suggestion:

where `--listen` specifies the server (optional address and) port.