I got an automatic update of Red Hat Enterprise Linux from 6.4 to 6.5 and after reboot my surprise was to find wireless network (wi-fi) disabled.
The first thing to look at was boot.log and it seems indeed the wireless support modules were unable to load. I will not go trough all my searches but point out the most important.
Forgot to mention, I have Lenovo T420 - it might be important for some.

I found the error in boot.log:

[root@florian log]# grep udev /var/log/boot.log 
Starting udev:                                           FATAL: Error inserting iwldvm (/lib/modules/2.6.32-431.11.2.el6.x86_64/kernel/drivers/net/wireless/iwlwifi/dvm/iwldvm.ko): Unknown symbol in module, or unknown parameter (see dmesg)
Retrigger failed udev events                               [  OK  ]

Trying to manually enable the modules was giving the same error:

[root@florian ~]# modprobe iwldvm
WARNING: Error inserting iwlwifi (/lib/modules/2.6.32-431.11.2.el6.x86_64/kernel/drivers/net/wireless/iwlwifi/iwlwifi.ko): Unknown symbol in module, or unknown parameter (see dmesg)
FATAL: Error inserting iwldvm (/lib/modules/2.6.32-431.11.2.el6.x86_64/kernel/drivers/net/wireless/iwlwifi/dvm/iwldvm.ko): Unknown symbol in module, or unknown parameter (see dmesg)

By running dmesg as recommended, it seems the problem is because of missing ipv6 support:

[root@florian ~]# dmesg|tail -n 2
mac80211: Unknown symbol unregister_inet6addr_notifier
mac80211: Unknown symbol register_inet6addr_notifier

Indeed, ipv6 is disabled:

[root@florian ~]# cat /etc/modprobe.d/disable-ipv6.conf
install ipv6 /bin/true
blacklist ipv6
install ip6_tables /bin/true
blacklist ip6_tables
[root@florian log]# lsmod|grep -i ipv6
[root@florian log]#

This is not OK, if I want to have ipv6 disabled, I have my reasons. Normally I won't do this but today I do not have time to dig deeper so I will just enable it and see if it works.
Will provide the permanent fix later so stay tuned.

Fix by enabling ipv6:

1. Comment out all lines in /etc/modprobe.d/disable-ipv6.conf (do not delete the file or any line - keep them there in case you want to revert):

[root@florian ~]# cat /etc/modprobe.d/disable-ipv6.conf
#install ipv6 /bin/true
#blacklist ipv6
#install ip6_tables /bin/true
#blacklist ip6_tables

2. Reboot.

3. Wireless should work now because ipv6 is enabled. Also boot.log and lsmod have the correct display:

[root@florian log]# lsmod|grep -i ipv6
ip6t_ipv6header         1792  2 
nf_conntrack_ipv6       8337  6 
nf_defrag_ipv6         11156  1 nf_conntrack_ipv6
nf_conntrack           79758  7 ipt_MASQUERADE,iptable_nat,nf_nat,nf_conntrack_ipv4,nf_conntrack_ftp,nf_conntrack_ipv6,xt_state
ip6_tables             18732  4 ip6table_mangle,ip6t_LOG,ip6t_ipv6header,ip6table_filter
ipv6                  317829  93 ip6table_mangle,ip6t_REJECT,nf_conntrack_ipv6,nf_defrag_ipv6,mac80211

[root@florian log]# grep udev /var/log/boot.log
Starting udev: [ OK ]
Retrigger failed udev events [ OK ]
[/code]

[root@florian log]# lsmod|grep iwl
iwldvm                135807  0 
mac80211              552581  1 iwldvm
iwlwifi                92090  1 iwldvm
cfg80211              619515  3 iwldvm,mac80211,iwlwifi