Could you please try if you get any other AVC? (I was unable to reproduce the issue - winbind doesn't seem to like virtual machines)?
Reproducing the issue with SELinux in permissive mode will show us all the permission winbind needs. Plese try the following>

#setenforce 0
<reproduce the issue>
#ausearch -m avc -ts recent
#setenforce 1

The problem is that I don't know what reproduces it.  It just happens when it happens like it did yesterday.  The report said:

SELinux is preventing winbindd from 'name_connect' accesses on the tcp_socket port 52774.

*****  Plugin catchall_boolean (89.3 confidence) suggests   ******************

If you want to allow nis to enabled
Then you must tell SELinux about this by enabling the 'nis_enabled' boolean.
You can read 'None' man page for more details.
Do
setsebool -P nis_enabled 1

*****  Plugin catchall (11.6 confidence) suggests   **************************

If you believe that winbindd should be allowed name_connect access on the port 52774 tcp_socket by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# grep winbindd /var/log/audit/audit.log | audit2allow -M mypol
# semodule -i mypol.pp

Additional Information:
Source Context                system_u:system_r:winbind_t:s0
Target Context                system_u:object_r:ephemeral_port_t:s0
Target Objects                port 52774 [ tcp_socket ]
Source                        winbindd
Source Path                   winbindd
Port                          52774
Host                          (removed)
Source RPM Packages           
Target RPM Packages           
Policy RPM                    selinux-policy-3.13.1-158.fc23.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 4.2.6-301.fc23.x86_64 #1 SMP Fri
                              Nov 20 22:22:41 UTC 2015 x86_64 x86_64
Alert Count                   231
First Seen                    2015-10-07 05:48:28 EDT
Last Seen                     2016-01-04 07:01:33 EST
Local ID                      42991ac8-471d-47bc-89ad-b9171fd55477

Raw Audit Messages
type=AVC msg=audit(1451908893.874:40613): avc:  denied  { name_connect } for  pid=1786 comm="winbindd" dest=52774 scontext=system_u:system_r:winbind_t:s0 tcontext=system_u:object_r:ephemeral_port_t:s0 tclass=tcp_socket permissive=0


Hash: winbindd,winbind_t,ephemeral_port_t,tcp_socket,name_connect

Lets ask samba folks.

It would be good to see winbindd logs around this connection. You can set 'log level = 100' to generate a lot of networking logs in Samba.

Where do I set "log level = 100"?  /etc/samba/smb.conf in [general] section?  Or somewhere else?

The section is called '[global]'.

I tried to set log level to 100 by commenting out my existing log level and adding a new one as such:

#log level = 0 auth:10 winbind:10
log level = 100 # auth:10 winbind:10

That left me unable to authenticate to the domain using "wbinfo -K <userid>":

$ wbinfo -K brian
Enter brian's password: 
plaintext kerberos password authentication for [brian] failed (requesting cctype: FILE)
Could not authenticate user [brian] with Kerberos (ccache: FILE)

wbinfo -K --krb5ccname=KEYRING brian

Why would making the "log level" change all of a sudden require me to supply "--krb5ccname=KEYRING" to wbinfo when the previous "log level" setting did not?

Description of problem:
Logging into AD domain

Version-Release number of selected component:
selinux-policy-3.13.1-158.15.fc23.noarch

Additional info:
reporter:       libreport-2.6.4
hashmarkername: setroubleshoot
kernel:         4.5.6-200.fc23.x86_64
type:           libreport

Description of problem:
Logging into an AD domain

Version-Release number of selected component:
selinux-policy-3.13.1-158.15.fc23.noarch

Additional info:
reporter:       libreport-2.6.4
hashmarkername: setroubleshoot
kernel:         4.5.6-200.fc23.x86_64
type:           libreport

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