TOOLS/PERF: Simplify Socket RTE initialization

[dmitrygx]

What

Simplify Socket RTE initialization.

Why ?

The code becomes clearer and it helps remove one goto label and reduce some code duplication.

How ?

1. Set sockfd from value connfd in case of server in loop over all IP interfaces in setup_sock_rte_p2p after listening sockfd was clsoed.
2. Print accept error through err_str as it is done for other operations.