gprs: Send PING and eventually reconnect

Currently, the reconnect mechanism relies on gsup_client_updown_cb
which in turn gets called based on the OS' view of connection state.

This patch adds a timer based PING mechanism that regularly sends
PING messages and forces a reconnect if a PONG message won't be
received until the next PING message is scheduled. The current ping
interval is 20s.

Sponsored-by: On-Waves ehf

Conflicts:
	openbsc/src/gprs/gprs_gsup_client.c

[hfreyther: Conflicts due the potential memleak fix by me. Removed
another TODO from the code as we stop the ping/pong timer]
2 files changed
tree: f04b6e49fc98b07c9f62993ce3a5f5c5ad202c99
  1. debian/
  2. hlrsync/
  3. linux-kernel/
  4. openbsc/
  5. wireshark/
  6. README