Fix a second cause of undersized pallocs for btree_gist indexes on macaddr.
Fix a second cause of undersized pallocs for btree_gist indexes on macaddr.

gbt_macad_union also allocated 12-byte structs where we really need 16.

Per report from Andres Freund.  No back-patch since there's no current
risk of a real problem.

xinzweb/gpdb,adam8157/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,yazun/postgres-xl,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,adam8157/gpdb,techdragon/Postgres-XL,50wu/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,oberstet/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,lisakowen/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,oberstet/postgres-xl,adam8157/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,ashwinstar/gpdb,50wu/gpdb,yazun/postgres-xl,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,ashwinstar/gpdb,oberstet/postgres-xl,yazun/postgres-xl,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,yazun/postgres-xl,ashwinstar/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,greenplum-db/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,zeroae/postgres-xl,techdragon/Postgres-XL,pavanvd/postgres-xl,pavanvd/postgres-xl,50wu/gpdb,techdragon/Postgres-XL,lisakowen/gpdb,ovr/postgres-xl,adam8157/gpdb,oberstet/postgres-xl,lisakowen/gpdb,yazun/postgres-xl,zeroae/postgres-xl,greenplum-db/gpdb,ovr/postgres-xl,ovr/postgres-xl,lisakowen/gpdb,ovr/postgres-xl,Postgres-XL/Postgres-XL,greenplum-db/gpdb,Postgres-XL/Postgres-XL,zeroae/postgres-xl,jmcatamney/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,Postgres-XL/Postgres-XL,techdragon/Postgres-XL,jmcatamney/gpdb,lisakowen/gpdb,xinzweb/gpdb