Fix compilation warning for gp_dispatch_keepalives GUC
This is the warning:
guc_gp.c:4063:4: warning: initialization of 'int' from 'void *'
makes integer from pointer without a cast [-Wint-conversion]
4063 |    NULL,
|    ^~~~
That happens because there was an extra field in the struct that
described gp_dispatch_keepalives_count GUC (introduced in
https://github.com/greenplum-db/gpdb/commit/d673b309ce571932fbf887ae25182d28dac913b7).
@@ -4060,7 +4060,6 @@ struct config_int ConfigureNamesInt_gp[] =
gettext_noop("This controls the number of consecutive keepalive retransmits that can be "
"lost before a QD/QE connection is considered dead. A value of 0 uses the "
"system default."),
- NULL,
GUC_NOT_IN_SAMPLE
},
&gp_dispatch_keepalives_count,
