mgmt: add FaceStatus::unsetExpirationPeriod()

For consistency with Route.

Change-Id: Ieac12ebd7fc7270c03d331c48747bd913f79fef9
Refs: #3903
diff --git a/src/mgmt/nfd/face-status.cpp b/src/mgmt/nfd/face-status.cpp
index df0521f..53ccf61 100644
--- a/src/mgmt/nfd/face-status.cpp
+++ b/src/mgmt/nfd/face-status.cpp
@@ -264,6 +264,14 @@
 }
 
 FaceStatus&
+FaceStatus::unsetExpirationPeriod()
+{
+  m_wire.reset();
+  m_expirationPeriod = nullopt;
+  return *this;
+}
+
+FaceStatus&
 FaceStatus::setNInInterests(uint64_t nInInterests)
 {
   m_wire.reset();