rdma: fix bug related to ring buffer

Fix a bug that caused some input packets to be dropped due to errors of
the type 'ip4 length > l2 length'. The change is related to the second
call to the rdma_device_input_bufs() function that happens when the end
of the ring buffer is reached.

Type: fix
Change-Id: I332d69ab22242b3443a0baca6e5dd86349a54765
Signed-off-by: Elias Rudberg <elias.rudberg@bahnhof.net>