selftests: drivers: hw: test rmon counters only on first interface

selftests: drivers: hw: test rmon counters only on first interface

The selftests in drivers/net are slowly transitioning to being able to
be used on systems with a single network interface. The first step for the
ethtool_rmon.sh test is to only validate that the rmon counters are
properly exported on the first interface supplied as an argument.

Remove the rmon_histogram calls which intend to test also the rmon
counters on the 2nd interface. This also removes the need for the remote
system, which should be used only to inject traffic, to also support
rmon counters.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Link: https://patch.msgid.link/20260330152933.2195885-6-ioana.ciornei@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>