Changes

gtp: allow packets with E-bit set

Do not drop packets early that have the bit for indicating presence of
next extension header set ("Unsupported packet flags 0x36").

With this patch, a packet with extension header gets into the "Check for
extension headers" code path. There the GGSN currently rejects all such
packages with an "Unsupported extension header" error log message, and
sends a Supported Extension Headers Notification to the SGSN.

Related: OS#6223
Change-Id: Ic62f95874a877a2f295765b807d7f23b011aeaa3