vrouter: VR socket ("fake Netlink") buffers are too small

Due to above there is need to alter the send's buffer size
(as it was originally 512bytes which is far smaller than original
Netlink implementation on linux.) It does not really affect the
receive buffer, which has its size altered anyway on the agent size.
Merge pull request #2 from Semihalf/fix-vrsock-buffer-size

vrouter: VR socket ("fake Netlink") buffers are too small