Currently, production code uses BpfMap type and TestBpfMap extends
BpfMap but this makes it diffcult to test because TestBpfMap loads the
JNI.
This CL updates to use IBpfMap type in the production code.
Upcoming CL updates TestBpfMap to implement IBpfMap instead of extending
BpfMap so that test can still use TestBpfMap but tests do not need to
load JNI.
Bug: 217624062
Test: atest BpfCoordinatorTest BpfNetMapsTest
Change-Id: Ie67e14bf5519fb4427474ecc0fda441877a9555f
73599a5f5d