netshaper: Add netshaper command

netshaper: Add netshaper command

Add support for the netshaper Generic Netlink family to
iproute2. Introduce a new command for configuring netshaper
parameters directly from userspace.

This interface allows users to set shaping attributes which
are passed to the kernel to perform the corresponding netshaper
operation.

Example usage:
$netshaper { set | show | delete } dev DEV \
           handle scope SCOPE [id ID] \
           [ bw-max BW_MAX ]

Internally, this triggers a kernel call to apply the shaping
configuration to the specified network device.

Currently, the tool supports the following functionalities:
- Setting bandwidth in Mbps, enabling bandwidth clamping for
  a network device that support netshaper operations.
- Deleting the current configuration.
- Querying the existing configuration.

Additional netshaper operations will be integrated into the tool
as per requirement.

This change enables easy and scriptable configuration of bandwidth
shaping for devices that use the netshaper Netlink family.

Corresponding net-next patches:
1) https://lore.kernel.org/all/cover.1728460186.git.pabeni@redhat.com/
2) https://lore.kernel.org/lkml/1750144656-2021-1-git-send-email-ernis@linux.microsoft.com/

Install pkg-config and libmnl* packages to print kernel extack
errors to stdout.

Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>