Clean-up: relayd: unused tcp keep alive config return value

Clean-up: relayd: unused tcp keep alive config return value

gcc 10.1.0 reports:
  tcp_keep_alive.c: In function \u2018tcp_keep_alive_init\u2019:
  tcp_keep_alive.c:519:9: warning: \u2018removed_return.58\u2019 is used uninitialized in this function [-Wuninitialized]
    519 |  return tcp_keep_alive_init_config(&support, &config);
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tcp_keep_alive_init is a constructor and, as such, should not return a
value. GCC warns that its return value is unused (although with a
somewhat strange warning message).

The return value of tcp_keep_alive_init_config is ignored as all
error paths log a suitable error and not much more can be done.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I912fe7e6c817edf77dd26bc7e18c0a14a9cbe94e