Unconditionally wait at least one delta cycle

tb/arp_ep.py

@@ -263,6 +263,7 @@ class ARPFrameSink():
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/baser_serdes_ep.py

@@ -375,6 +375,7 @@ class BaseRSerdesSink(object):
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/eth_ep.py

@@ -241,6 +241,7 @@ class EthFrameSink():
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/gmii_ep.py

@@ -193,6 +193,7 @@ class GMIISink(object):
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/ip_ep.py

@@ -383,6 +383,7 @@ class IPFrameSink():
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/mii_ep.py

@@ -201,6 +201,7 @@ class MIISink(object):
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/udp_ep.py

@@ -476,6 +476,7 @@ class UDPFrameSink():
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout:

tb/xgmii_ep.py

@@ -258,6 +258,7 @@ class XGMIISink(object):
         return not self.queue
 
     def wait(self, timeout=0):
+        yield delay(0)
         if self.queue:
             return
         if timeout: