MINOR: log: provide a way to override logger->profile from process_send_log_ctx

MINOR: log: provide a way to override logger->profile from process_send_log_ctx

In process_send_log(), now also consider the ctx if ctx->profile != NULL

In that case, we do as if logger->prof was set, but we consider
ctx->profile in priority over the logger one. What this means is that
it will become possible to pass ctx.profile to a profile that will be
used no matter what to generate the log payload.

This is a pre-requisite to implement optional "profile" argument for
do-log action