Fix integer overflow in build_read_multi_rsp

Local variables tracking structure size in build_read_multi_rsp are of
uint16 type but accept a full uint16 range from function arguments while
appending a fixed-length offset.  This can lead to an integer overflow
and unexpected behavior.

Change the locals to size_t, and add a check during reasssignment.

Bug: 273966636
Test: atest bluetooth_test_gd_unit, net_test_stack_btm
Tag: #security
Ignore-AOSP-First: Security
Change-Id: I3a74bdb0d003cb6bf4f282615be8c68836676715
(cherry picked from commit 70a4d628)