CNB96: rtnetlink: reduce RTNL pressure for dumps

JIRA: https://issues.redhat.com/browse/RHEL-62123

Description: The patch-set is a common dependency for follow-up MRs. The goal for this and the other MRs is to remove dependency on RTNL big-lock as much as possible.

Commits:

75ea27d0d622 ("net: introduce a function to check if a netdev name is in use")
145c7a793838 ("ipv6: make mc_forwarding atomic")
70986397a15b ("net: move from strlcpy with unused retval to strscpy")
311cca40661f ("net: fix ifname in netlink ntf during netns move")
7663d522099e ("net: check for altname conflicts when changing netdev's netns")
1a83f4a7c156 ("net: avoid UAF on deleted altname")
8e15aee62161 ("net: move altnames together with the netdevice")
3920431d98a9 ("selftests: net: add very basic test for netdev names and namespaces")
d09486a04f5d ("net: fix removing a namespace with conflicting altnames")
723de3ebef03 ("net: free altname using an RCU callback")
e353ea9ce471 ("rtnetlink: prepare nla_put_iflink() to run under RCU")
4ad268136421 ("ipv6: prepare inet6_fill_ifla6_attrs() for RCU")
8afc7a78d55d ("ipv6: prepare inet6_fill_ifinfo() for RCU protection")
ac14ad9755d4 ("ipv6: use xarray iterator to implement inet6_dump_ifinfo()")
6647b338fc5c ("netlink: fix netlink_diag_dump() return value")
b5590270068c ("netlink: hold nlk->cb_mutex longer in __netlink_dump_start()")
e39951d965bf ("rtnetlink: change nlk->cb_mutex role")
386520e0ecc0 ("rtnetlink: add RTNL_FLAG_DUMP_UNLOCKED flag")
69fdb7e411b6 ("ipv6: switch inet6_dump_ifinfo() to RCU protection")
22e36ea9f5d7 ("inet: allow ip_valid_fib_dump_req() to be called with RTNL or RCU")
0ac3fa0c3b36 ("nexthop: allow nexthop_mpath_fill_node() to be called without RTNL")
4ce5dc9316de ("inet: switch inet_dump_fib() to RCU protection")
74808e72e0b2 ("rtnetlink: make rtnl_fill_link_ifmap() RCU ready")
0ec4e48c3a23 ("rtnetlink: provide RCU protection to rtnl_fill_prop_list()")
460b0d33cf10 ("inet: bring NLM_DONE out to a separate recv() again")
8d8b1a422c46 ("net: annotate data-races around dev->if_port")

Signed-off-by: Ivan Vecera ivecera@redhat.com