Increase global binder proxy limit to 25k.

We know that the current per-uid proxy limit mechanism is not entirely
accurate because of delayed GC; in the worst case, this means that an
app can have twice the number of allowed proxies outstanding (~13k
proxies). To account for this, slightly bump the limit at which we
crash.

Bug: 198340142
Test: N/A
Change-Id: Ic6973a2dd60434b3f92041304522fcffb4fbbfd8