dnsmasq: uprev to 2.6.3

A minimum dnsmasq version of 2.5.9 is required deal with IPv6 link local
addresses. So instead of just going to the minimum version, we can go
all the way to 2.6.3.

As part of this update, the following changes have been made in addition to
the pure version update:

  - PR is dropped in favour of PRSERVER functionality
  - dhcp_release is added to the default build, since it is used in the
    cleanup phase for virtual machines.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Joe MacDonald <joe@deserted.net>