snprintf in libpcap

[Michael Richardson]

Back in 2016, we note in the CHANGES:
    Replace sprintf() with pcap_snprintf().

but, we have no prototype for this, and apparently no definition, and we use
snprintf() everywhere.  I'm trying to merge Ray's changes which are rebased
into pull request #914.

I think that we just use "snprintf()" now.

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]   Michael Richardson, Sandelman Software Works        |    IoT architect   [
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