Improve comment in postgresql.conf.sample.
The Unix manual section that "man tcp" appears in varies, so let's
just leave it out of the command to run.
# (change requires restart)
# - TCP settings -
-# see "man 7 tcp" for details
+# see "man tcp" for details
#tcp_keepalives_idle = 0 # TCP_KEEPIDLE, in seconds;
# 0 selects the system default
