localextra.rules: Change serial port permissions
localextra.rules: Change serial port permissions

Current permissions of serial port devices is 666, which is a security
concern. Change the permissions to 660.

Signed-off-by: Shreyas Bethur <4d3f5c7320c9233fd2161302bf379a62a72814c8@ni.com>
Acked-by: Ken Sharp <e6c8ad8f54d15df4645e8aaf3f7a209bc3688570@ni.com>
Acked-by: Karthik Manamcheri <ed70b4b939d17eeebf52b77404c3f28ede6c7641@ni.com>
Natinst-CAR-ID: 437447
Natinst-Reviewboard-ID: 82236

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt