error_report() terminates the message with a newline.  Strip it it
from its arguments.

This fixes a few error messages lacking a newline:
net_handle_fd_param()'s "No file descriptor named %s found", and
tap_open()'s "vnet_hdr=1 requested, but no kernel support for
IFF_VNET_HDR available" (all three versions).

There's one place that passes arguments without newlines
intentionally: load_vmstate().  Fix it up.

aliguori: fix uninitialized use of pcap_len
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>