Improve var names in get_memory

Backport from master
Use updated get_memory var names 

Backport to 2.1
Dummynet does not require burst size specification

Dummynet traffic shaper does not require burst size specification and
assumes 0 if not specified. Allow user to leave burst field blank, if
not blank the must be numeric
add option to send prefix hint for requesting desired prefix length for delegation

This change adds an option on the interfaces page for sending a prefix hint for the selected delegation size. If enabled, a "prefix" field requesting :: with the appropriate prefix length (64 - dhcp6-ia-pd-len) is added to the "id-assoc pd" entry in the dhcp6c config file. This hint is required for requesting prefixes shorter than /64 from Comcast.
touch up text, s/nat/NAT/
Use hw.physmem when calculating pfsense_default_state_size

hw.physmem is the actual amount of memory that FreeBSD/pfSense can get its hands on, so use this for the calculation.
Backport to 2.1
Use new names for get_memory parameters
Use physmem and realmem from get_memory() in the appropriate places

Backport to 2.1
Merge pull request #791 from jean-m-cyr/RELENG_2_1

Dummynet does not require burst size specification
Merge pull request #792 from razzfazz/RELENG_2_1

add option to send prefix hint for requesting desired prefix length for ...
fix text
Resolves #3177. Do a filter reconfigure if the dynds ipsec hosts are present and being reloaded.
Make sure RRD data is restored from backup before upgrading data and a new backup is done after. It should fix #2159
Fix issue reported on http://forum.pfsense.org/index.php/topic,66160.0.html
Correct typo on variable name
Disable state killing on gateway failure by default for new configs.
Clarify the text describing the option while here.
Fix #3004:

. Create a function to replace strings on deep associative arrays
. Use the recent created function array_replace_values_recursive to fix
  VIP interface names instead of touch config.xml directly
Bring back static routes to fix issues reported on Ticext #3179
Merge pull request #794 from phil-davis/RELENG_2_1

Backport get_memory changes to 2.1
Merge pull request #790 from shahidsheikh/RELENG_2_1

 #3174 Added handling of gateway groups in openvpn_restart