Revert "tipc: check the bearer min mtu properly when setting it by netlink"

This reverts commit 2937127d which is
commit 35a089b5 upstream.

It breaks the Android kernel ABI and is not needed for Android devices,
so it is safe to revert for now.  If it is determined that it is needed
in the future, it can be brought back in an abi-preserving way.

Bug: 161946584
Change-Id: Iac2aaf58f7e53317626d0f7f125b55e72228c770
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>