Fix: Generation of bytecode longer than 32768 bytes fails

Fix: Generation of bytecode longer than 32768 bytes fails

The bytecode buffer length field is currently limited to a uint16_t.  A
larger buffer, lttng_filter_bytecode_alloc, is the underlying storage
for the bytecode.

The current allocation policy dictate that the alloc buffer size must be
doubled everytime the bytecode size plus padding exceeds its capacity.

A problem arise when generating bytecode larger than 32768 bytes.

e.g.:

Legend
* required_len: new bytecode len
* old_len: current alloc_len
* new_len: new alloc_len

src/bin/lttng/lttng enable-event event:bla -s foo -u --filter "`perl -e 'print "intfield" . " && 1" x2730'`"
UST event ust_tests_hello:tptest created in channel channel0
[debug liblttng-ctl] Generating IR... [debug liblttng-ctl] done
[debug liblttng-ctl] Validating IR... [debug liblttng-ctl] done
[debug liblttng-ctl] Generating bytecode... required_len = 11, old_len = 4, new_len = 16
required_len = 7, old_len = 4, new_len = 8
required_len = 16, old_len = 8, new_len = 16
required_len = 19, old_len = 16, new_len = 32
required_len = 40, old_len = 32, new_len = 64
required_len = 67, old_len = 64, new_len = 128
required_len = 136, old_len = 128, new_len = 256
required_len = 259, old_len = 256, new_len = 512
required_len = 520, old_len = 512, new_len = 1024
required_len = 1027, old_len = 1024, new_len = 2048
required_len = 2056, old_len = 2048, new_len = 4096
required_len = 4099, old_len = 4096, new_len = 8192
required_len = 8200, old_len = 8192, new_len = 16384
required_len = 16387, old_len = 16384, new_len = 32768
required_len = 32776, old_len = 32768, new_len = 65536 <-- Overflow 16-bits
Generate bytecode error
Error: Error setting filter

The last new_len exceed the range of 16-bits values. In order to support
the largest bytecode length (65535), the underlying alloc buffer len
must be able to store more than 65535. Fix this by using a uint32_t for
alloc_len.

Also, add a check to ensure that a bytecode longer than
LTTNG_FILTER_MAX_LEN (65535) bytes can't be generated.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>