Added implementation of sendmsg/recvmsg/inject for usdf dgram ep.

Currently sendmsg/recvmsg just directly call their counterparts for
sendv/recvv. Code need to be added to handle different flags such
as FI_COMPLETION/FI_INJECT and so on.

Also fixed some whitespace errors.

Signed-off-by: Xuyang Wang <xuywang@cisco.com>