[mac] add enhanced frame pending (#4334)

This commit adds enhanced frame pending feature of Thread 1.2. This
requires the platform radio driver to correctly set frame pending bit
for Data frames and MAC Data Request frames.

tests/scripts/thread-cert/common.py

@@ -37,6 +37,8 @@ import ipaddress
 # Map of 2 bits of parent priority.
 pp_map = {1: 1, 0: 0, 3: -1, 2: -2}
 
+UDP_TEST_PORT = 12345
+
 
 # Get the signed parent priority from the byte that parent priority is in.
 def map_pp(pp_byte):