tty: n_smux: Add throughput metrics to unit tests
tty: n_smux: Add throughput metrics to unit tests

Add throughput metrics to unit tests to enable profiling the performance
of SMUX round-trip messaging.

Change-Id: I1eb552ca53358ece9f95a99a340409a4464877fb
Signed-off-by: Eric Holmberg <5000aa55685d659e1f7f26ece526f9c7021ab484@codeaurora.org>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas