adb: rationalize types.

Use fixed length types for structs going over the wire, constify
arguments where possible, use char* instead of unsigned char* for
apacket data, and assorted other refactoring.

Bug: http://b/29273531
Test: python test_device.py with every combination of old/new adb and adbd
Change-Id: I0b6f818a32be5386985aa4519f542003cf427f9d
diff --git a/adb/adb.cpp b/adb/adb.cpp
index 89a20f0..29d6e65 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -94,6 +94,18 @@
     abort();
 }
 
+uint32_t calculate_apacket_checksum(const apacket* p) {
+    const unsigned char* x = reinterpret_cast<const unsigned char*>(p->data);
+    uint32_t sum = 0;
+    size_t count = p->msg.data_length;
+
+    while (count-- > 0) {
+        sum += *x++;
+    }
+
+    return sum;
+}
+
 apacket* get_apacket(void)
 {
     apacket* p = reinterpret_cast<apacket*>(malloc(sizeof(apacket)));