…ccessible to all protocols

Adds definitions for the IP fragmentation flags
Modifies the fragmentation check for incoming frames to drop both the first and later fragments.
Sets the "don't fragment" flag for all outgoing IP frames ( ICMP, DNS, UDP, TCP )
Removes ipGET_UDP_PAYLOAD_OFFSET_FOR_FRAGMENT as it appears obsolete. The stack never outputs fragments.

…0xF000 -> 0x1FFF and 0xE000 )

Adds a configuration define ( ipconfigADVERTISE_DONT_FRAGMENT_FLAG ) as suggested by htibosch with a default value of zero for backwards compatibility
Updates the comment that explains the discarding of incoming fragments as discussed with Aniruddha Kanhere

fixes a typo in FreeRTOSIPConfigDefaults.h

…ggestion.

…MENT