Changes

sctp_{client,server}: disable Nagle by setting sctp_nodelay

The Nagle's algorithm [1] works by combining a number of small outgoing
messages and sending them all at once.  It's enabled by default when
opening a socket.  While it helps to reduce the network congestion by
reducing the number of outgoing packets, it comes at the cost of
increased delay.  Disable it by setting sctp_nodelay to true.

[1] https://en.wikipedia.org/wiki/Nagle%27s_algorithm

Change-Id: I6058a593a617d67d479eea0673d899a5da2d49bf
Related: SYS#7288

s1gw_metrics: make exometer_report_statsd less verbose

When running osmo-s1gw with {logger_level, debug}, this module clogs
the logging output with dozens of "Report metric ..." lines.  This
makes debugging osmo-s1gw harder, so let's force it to use info.

Change-Id: I317680252d052f6435d870d27ca51514ca5f0c09