Check to ensure UDP-encap is used only for IPv4

This commit checks if UDP-encapsulation is used
for unsupported address family and throws
IllegalArgumentException when it happens.

Bug: 74213459
Test: Tests added in testCreateTransportModeTransformWithEncap
      and testCreateTunnelModeTransformWithEncap.
      Command: runtest frameworks-net
      Verified on taimen.
Change-Id: I10c01f2bad6aca23430849ea9ef6c1eb157ae131