Revert "Add config to use lower of IPv4/IPv6 MTU values"

This reverts commit dc7260ad33d3d535cb27ef0e287892baba6265bc.
AT&T MTU fix is live, so this change can be reverted now.

Bug: 169608987
Test: atest DataConnectionTest
Change-Id: I60a350960bb14242efd5dca1b93b633e395e7376
1 file changed