rdma: Add filtering infrastructure

rdma: Add filtering infrastructure

This patch adds general infrastructure to RDMAtool to handle various
filtering options needed for the downstream resource tracking patches.

The infrastructure is generic and stores filters in list of key<->value
entries. There are three types of filters:

1. Numeric - the values are intended to be digits combined with '-' to
mark range and ',' to mark multiple entries, e.g. pid 1-100,234,400-401
is perfectly legit filter to limit process ids.

2. String - the values are consist from strings and "," as a denominator.

3. Link - special case to allow '/' in string to provide link name, e.g.
link mlx4_1/2.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>