Add recv callback to transport layer to better facilitate code reuse and
readability and for symmetry with send callback. Move recv_dgram and
recv_stream to udp_recv and lsock_recv, respectively, and make the
beforementioned functions recv callbacks for the udp and lsock transports,
respectively.
Consolidate the check_priv* functions in their relevant trans*.c source to
limit scope/use.
Note: this code is roughly based content from the submitter, although this
was modified to be more of a direct move from snmpd/main.c to the trans_*.c
sources, and to reduce unnecessary static function declarations.
MFC after: 2 weeks
Submitted by: Thor Steingrimsson <thor.steingrimsson@isilon.com>
Sponsored by: Dell EMC Isilon
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