genl: modify genl_ctrl_resolve and friends to allow for module auto-loading

genl: modify genl_ctrl_resolve and friends to allow for module auto-loading

Generic netlink has the ability to autoload modules in response to a request for
a family.  Currently libnl uses a GETFAMILY call with the NLM_F_DUMP flag to
list all the available families, but doing so neglects the possibility of an
autoloaded module.  This patch modifies the genl code to probe the kernel for a
specific family rather than dumping a list of all the currenlty available ones,
making autoload work properly.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Thomas Graf <tgraf@redhat.com>