vdptool: Add libnl libs to build

Add LIBNL_LIBS flags to fix the following build warning,

libtool: link: gcc -Wall -Werror -Wextra -Wformat=2 -I/usr/include/libnl3 -g -O2 -o .libs/vdptool vdptool.o lldp_util.o qbg/vdp22_clif.o  /home/john/git/lldp/lldpad/.libs/liblldp_clif.so ./.libs/liblldp_clif.so -Wl,-rpath -Wl,/usr/local/lib
lldp_util.o: In function `is_macvtap':
/home/john/git/lldp/lldpad/lldp_util.c:677: undefined reference to `nlmsg_parse'
/home/john/git/lldp/lldpad/lldp_util.c:689: undefined reference to `nla_parse_nested'

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
RFC - Support for get-tlv in vdptool and VDP22

This commit has the following changes:
a. Change in VDP22 and vdptool to support get-tlv. This actually refers to
get-vsi. Support for querying and printing all VSI's, partial VSI's is added.
The vdptool man page document is also modified accordingly.
b. The response from lldpad (VDP22) is modified to support to the
len, key, len, value format. Earlier, only the meessage to VDP22 has the
format. The response from VDP22 followed the comma separated format for VSI
parameters.
c. Fix some formatting issues

Signed-off-by: padkrish <padkrish@cisco.com>
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>