phy: Allow set netns by fd

phy: Allow set netns by fd

Added possibility to change network namespace
for phy device by network namespace name from
/var/run/netns or by absolute file path:

iw phy XXX set netns name <nsname>

iw tries to open fd of given nsname from /var/run/netns
or by absoute path if nsname contains "/".

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>