nvme: increase size of uevent buffer to 1MB

In production environments, there could be large numbers
of uevents other than nvme hotplug events.  We want to
ensure we never lose an nvme uevent due to ENOBUFS
(i.e. overflow).  So allocate a bigger receive buffer
for the netlink socket to ensure we never lose any events.
We only allocate one netlink socket per SPDK application,
so the extra memory consumption is not really a concern.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: I663fbb093516a01a8980a1517245f92d8c76f7aa
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/4070


Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>